Inhibitors (PLIs) against snake venom gland phospholipases A(2) (PLA(2)s) have been found in their sera. A cDNA encoding a PLI from Trimeresurus flavovirdis (Tf, habu snake, Crotalinae) serum, cPLI-A, was isolated from the Tf liver cDNA library and sequenced. Northern blot analysis with cPLI-A showed that PLIs are expressed only in liver. Genes for PLIs, gPLI-A and gPLI-B, were isolated from the Tf genomic DNA library and their nucleotide (nt) sequences were determined. The genes consisted of four exons and three introns, and exon 4 encoded the carbohydrate recognition domain (CRD)-like motif. Comparison of the nt sequences between gPLI-A and gPLI-B showed that these genes are highly homologous, including introns, except that exon 3 is rich in nonsynonymous nt substitutions which are almost four times as frequent as synonymous nt substitutions. This evolutionary feature of PLI genes is different from that of venom gland PLA(2) isozyme genes in which nonsynonymous nt substitutions are spread over the entire mature protein-coding region. (C) 1997 Elsevier Science B.V.