['Little is known of the light chains associated to heavy chains in secretions immunoglobulins. We investigated the partition of light chains in a mucosal fluid of easy access and major physiologic importance: human milk.', 'This study provides a sequential analysis of IgA, lambda and kappa chains levels in human milk during the first days of lactation. The levels of IgA alpha-chain and of lambda and kappa light chains of immunoglobulins were assayed in 162 samples of normal human milk collected during the first night of lactation, using a classical immunonephelometric assay. A specific enzyme-linked immunosorbent assay was developed to specifically measure the levels of IgA-linked light chains, yielding similar values. Ten samples of normal human serum obtained from healthy adults were tested in parallel.', 'The highest levels were observed during the first 3 days of lactation, and a plateau appeared for the three proteins after day 4. Mean lambda chains levels were consistently higher than these of kappa chains, resulting in a reversed kappa/lambda ratio, significantly different from the classical 2:1 serum ratio confirmed with this method on control samples.'] Does sequential assay of human milk immunoglobulins show a predominance of lambda chains?