A humanized variant of a camelid-derived antibody comprising a camelid VH domain and a camelid VL domain of either the lambda light chain class (Vλ) or the kappa light chain class (Vκ), wherein said humanized variant is obtained by replacement of one or more amino acids of the original camelid VH domain and/or the original camelid VL domain, said one or more replacements being selected from the following (numbering according to Kabat): H1 replaced with Q or E.; H7 replaced with S; H11 replaced with V; H12 replaced with K; H13 replaced with K, R or Q; H14 replaced with P; H29 replaced with V or F; H30 replaced with S; H37 replaced with V, I or F; H40 replaced with A; H48 replaced with I; H67 replaced with V; H68 replaced with T; H69 replaced with M, I or S; H71 replaced with R, V, A, E or T; H74 replaced with S or A; H77 replaced with S or T; H78 replaced with V, L or A; H80 replaced with M; H81 replaced with K; H83 replaced with R or K; H84 replaced with A or T; H85 replaced with A; H86 replaced with D; H94 replaced with R, K or T; H108 replaced with M, L or T; H5 replaced with L or V; H82b replaced with S; H89 replaced with V or L; H93 replaced with A or T; for a camelid VL domain of the lambda light chain class (Vλ): L1 replaced with S; L2 replaced with Y; L3 replaced with E; L7 replaced with D, P or L; L8 replaced with R, P, A, S, L or H; L9 replaced with P or A; L11 replaced with A, V, S, F, L or H; L14 replaced with T, S or A; L15 replaced with P, L or T; L17 replaced with Q, E or A; L18 replaced with R, S or K; L19 replaced with V, P or A; L20 replaced with R or S; L39 replaced with H or P; L40 replaced with P; L42 replaced with K or T; L47 replaced with M; L58 replaced with V; L59 replaced with P or S; L60 replaced with D or E; L66 replaced with S, N or T; L67 replaced with S, L or P; L69 replaced with T or N; L70 replaced with T, M, I or A; L71 replaced with V, A or T; L72 replaced with S, I, T or L; L74 replaced with A or G; L76 replaced with S or T; L78 replaced with V, A, T or I; L80 replaced with S, A, T or P; L84 replaced with A or S; L103 replaced with K; L38 replaced with Q; L44 replaced with P; L46 replaced with L; L49 replaced with Y; for a camelid VL domain of the kappa light chain class (Vκ): K1 replaced with A, D or N; K4 replaced with L or M; K7 replaced with S or T; K9 replaced with L or D; K11 replaced with V or L; K12 replaced with K, P, A or S; K13 replaced with K or V; K14 replaced with T; K15 replaced with V, L or T; K18 replaced with P, R or Q; K19 replaced with A; K36 replaced with Y, F or L; K39 replaced with K; K42 replaced with K; K43 replaced with A, P or V; K45 replaced with K; K46 replaced with L or R; K58 replaced with V; K63 replaced with S; K68 replaced with G; K70 replaced with D or E; K77 replaced with S or C; K78 replaced with L; K79 replaced with Q or E; K80 replaced with P, A or S; K83 replaced with F, V or I; K100 replaced with Q; K103 replaced with K; K104 replaced with V; K106 replaced with I; K3 replaced with Q or R. H1 replaced with Q or E.; H7 replaced with S; H11 replaced with V; H12 replaced with K; H13 replaced with K, R or Q; H14 replaced with P; H29 replaced with V or F; H30 replaced with S; H37 replaced with V, I or F; H40 replaced with A; H48 replaced with I; H67 replaced with V; H68 replaced with T; H69 replaced with M, I or S; H71 replaced with R, V, A, E or T; H74 replaced with S or A; H77 replaced with S or T; H78 replaced with V, L or A; H80 replaced with M; H81 replaced with K; H83 replaced with R or K; H84 replaced with A or T; H85 replaced with A; H86 replaced with D; H94 replaced with R, K or T; H108 replaced with M, L or T; H5 replaced with L or V; H82b replaced with S; H89 replaced with V or L; H93 replaced with A or T; L1 replaced with S; L2 replaced with Y; L3 replaced with E; L7 replaced with D, P or L; L8 replaced with R, P, A, S, L or H; L9 replaced with P or A; L11 replaced with A, V, S, F, L or H; L14 replaced with T, S or A; L15 replaced with P, L or T; L17 replaced with Q, E or A; L18 replaced with R, S or K; L19 replaced with V, P or A; L20 replaced with R or S; L39 replaced with H or P; L40 replaced with P; L42 replaced with K or T; L47 replaced with M; L58 replaced with V; L59 replaced with P or S; L60 replaced with D or E; L66 replaced with S, N or T; L67 replaced with S, L or P; L69 replaced with T or N; L70 replaced with T, M, I or A; L71 replaced with V, A or T; L72 replaced with S, I, T or L; L74 replaced with A or G; L76 replaced with S or T; L78 replaced with V, A, T or I; L80 replaced with S, A, T or P; L84 replaced with A or S; L103 replaced with K; L38 replaced with Q; L44 replaced with P; L46 replaced with L; L49 replaced with Y; K1 replaced with A, D or N; K4 replaced with L or M; K7 replaced with S or T; K9 replaced with L or D; K11 replaced with V or L; K12 replaced with K, P, A or S; K13 replaced with K or V; K14 replaced with T; K15 replaced with V, L or T; K18 replaced with P, R or Q; K19 replaced with A; K36 replaced with Y, F or L; K39 replaced with K; K42 replaced with K; K43 replaced with A, P or V; K45 replaced with K; K46 replaced with L or R; K58 replaced with V; K63 replaced with S; K68 replaced with G; K70 replaced with D or E; K77 replaced with S or C; K78 replaced with L; K79 replaced with Q or E; K80 replaced with P, A or S; K83 replaced with F, V or I; K100 replaced with Q; K103 replaced with K; K104 replaced with V; K106 replaced with I; K3 replaced with Q or R.