A prostate-specific membrane antigen (PSMA)-specific binding protein, wherein the PSMA-specific binding protein is a lipocalin 2 -derived binding protein and binds to PSMA with a K D of 10 nM or lower, wherein the PSMA-specific binding protein comprises or consists of frame regions and loop regions as represented in formula I: Frame 1 - Loop 1 - Frame 2 - Loop 2 - Frame 3 - Loop 3 - Frame 4 - Loop 4 - Frame 5 (formula I), wherein the frame regions consist of the following amino acid sequences: Frame 1 consists of an amino acid sequence consisting of the sequence of formula II: x 1 - (H/Q) - x 2 (formula II); Frame 2 consists of an amino acid sequence consisting of the sequence of formula III: S - x 3 - (K/N) - x 4 - N - x 5 (formula III); Frame 3 consists of an amino acid sequence consisting of the sequence of formula IV: Y - x 6 - T - x 7 - A - x 8 - (S/C) - (Q/R) - x 9 - (F/Y) - x 10 (formula IV); Frame 4 consists of an amino acid sequence consisting of the sequence of formula V: G - x 11 - (N/S) - x 12 (formula V); Frame 5 consists of an amino acid sequence consisting of the sequence of formula VI: x 13 - I - x 14 -(E/K) - x 15 (formula VI); wherein x 1 to x 15 consist of the following amino acid sequences or are a variant thereof, wherein the overall sum of all variations of x 1 to x 15, as compared to the specifically cited sequences presented for x 1 to x 15 above, does not exceed 12 amino acid variations: x 1 consists of the amino acid sequence QDSTSDLIPAPPLSKVPLQQNFQDNQF (SEQ ID NO:8) or an N-terminal deletion fragment thereof, wherein no more than 6 amino acids are deleted; and x 2 consists of the amino acid sequence GKWYVVGLA (SEQ ID NO:9); x 3 consists of the amino acid sequence ATIYEL (SEQ ID NO:10); x 4 consists of the amino acid sequence EDKSYNVT (SEQ ID NO:11); x 5 consists of the amino acid V; x 6 consists of the amino acid Y; x 7 consists of the amino acid I; x 8 consists of the amino acid sequence TFVPG (SEQ ID NO:12); x 9 consists of the amino acid sequence PGE; x 10 consists of the amino acid sequence TL; x 11 consists of the amino acid sequence LVRWSTNY (SEQ ID NO:13); x 12 consists of the amino acid sequence QHAMVFFK (SEQ ID NO:14); x 13 consists of the amino acid F; x 14 consists of the amino acid sequence ITLYGRTKELTS (SEQ ID NO:15); and x 15 consists of the amino acid sequence LKENFIRFSKSLGLPENHIVFPVPIDQCIDG (SEQ ID NO:16) or a C-terminal deletion fragment thereof, wherein no more than 3 amino acids are deleted; and wherein the loop regions consist of the following amino acid sequences: Loop 1 consists of the amino acid sequence GNVILREDKDPYKM (SEQ ID NO:19) or GNMILREDKDPYKM (SEQ ID NO:20); Loop 2 consists of the amino acid sequence RFYLNKC (SEQ ID NO:21), RFYLKKC (SEQ ID NO:22), RYYLNKC (SEQ ID NO:23) or RYYLKKC (SEQ ID NO:24); Loop 3 consists of the amino acid sequence GTIKSGPGKTS (SEQ ID NO:25) or GTIKSGPGDTS (SEQ ID NO:26); and/or Loop 4 consists of the amino acid sequence EVQQNREW (SEQ ID NO:27). x 1 consists of the amino acid sequence QDSTSDLIPAPPLSKVPLQQNFQDNQF (SEQ ID NO:8) or an N-terminal deletion fragment thereof, wherein no more than 6 amino acids are deleted; and x 2 consists of the amino acid sequence GKWYVVGLA (SEQ ID NO:9); x 3 consists of the amino acid sequence ATIYEL (SEQ ID NO:10); x 4 consists of the amino acid sequence EDKSYNVT (SEQ ID NO:11); x 5 consists of the amino acid V; x 6 consists of the amino acid Y; x 7 consists of the amino acid I; x 8 consists of the amino acid sequence TFVPG (SEQ ID NO:12); x 9 consists of the amino acid sequence PGE; x 10 consists of the amino acid sequence TL; x 11 consists of the amino acid sequence LVRWSTNY (SEQ ID NO:13); x 12 consists of the amino acid sequence QHAMVFFK (SEQ ID NO:14); x 13 consists of the amino acid F; x 14 consists of the amino acid sequence ITLYGRTKELTS (SEQ ID NO:15); and x 15 consists of the amino acid sequence LKENFIRFSKSLGLPENHIVFPVPIDQCIDG (SEQ ID NO:16) or a C-terminal deletion fragment thereof, wherein no more than 3 amino acids are deleted;