Mutations of the glucokinase gene result in early-onset familial Type 2 (non-insulin-dependent) diabetes mellitus, and several members of the mutant glucokinase kindreds were originally diagnosed as having gestational diabetes. This study examined the glucokinase gene in 270 American Black women, including 94 with gestational diabetes whose diabetes resolved after pregnancy (gestational diabetes only), 77 with gestational diabetes who developed Type 2 diabetes after pregnancy (overt diabetes), and 99 normal control subjects who were recruited during the peripartum period. Two simple sequence repeat polymorphisms flanking either end of the glucokinase gene were evaluated. No association was found between glucokinase alleles and gestational diabetes only or overt diabetes, after adjustment for multiple comparisons. To detect single base changes, all 11 exons and proximal islet and liver promoter regions were examined by polymerase chain reaction plus single-stranded conformational polymorphism analysis in 45 gestational diabetes only patients who had not yet developed Type 2 diabetes. Nine coding region variants were identified: Ala11 (GCC) to Thr11 (ACC) in islet exon 1, and 8 variants either in untranslated regions or in the third base of a codon. Four variant sites were found in introns, but none in splicing consensus sequences. Analysis of the promoter regions revealed two common variants, G-->A at islet -30 (24%), and G-->A at liver -258 (42%). The frequencies of the promoter variants, determined by allele specific polymerase chain reaction analysis, but did not differ among the three groups. Thus, no significant coding sequence glucokinase mutations were found in 90 alleles from 45 patients with gestational diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)