An effort has been made to confirm the report [Dubinin, N. P. & Altukhov, Y. P. (1979) Proc. Natl. Acad. Sci. USA 76, 5226-5229] that children born prematurely or exhibiting congenital defects can be shown to exhibit relatively high frequencies of rare (nonpolymorphic) electrophoretic variants of proteins and that a large proportion of these variants are due to mutation in either the father or the mother. In a series of 178 children who were comparable with those described in the earlier report, we failed to encounter a high frequency of these variants in some 5341 determinations involving 45 proteins, nor were any mutations observed. Data from 1583 determinations of enzyme activity on a subset of the panel of proteins were also unremarkable. We are thus unable to confirm the earlier report.