Aims/hypothesis. The identification of mutations in hepatocyte nuclear factors-1α, –4α, –1β and insulin promoter factor-1 in maturity onset diabetes of the young (MODY) has highlighted the role that transcription factors may have in the development of diabetes. This result has focused molecular genetic studies of diabetes on other transcription factors expressed in the pancreatic beta cell. The basic helix-loop-helix transcription factor BETA2/NEUROD1 (gene symbol, NEUROD1) and the paired box homeodomain transcription factor PAX4 (PAX4) have an important role in islet and beta-cell development. We have examined the contribution of these transcription factors to the development of MODY and late-onset Type II (non-insulin-dependent) diabetes mellitus. Methods. Linkage studies have been done in MODY families reported to have no mutations in the five known MODY genes and in affected sibling pairs from families with late-onset Type II diabetes. Mutation screening of the coding regions of both genes was also realised by SSCP followed by sequencing in MODY patients and in probands with late-onset Type II diabetes. Results. There was no evidence of linkage with the markers for NEUROD1 and PAX4 either with MODY or late-onset Type II diabetes. Mutation screening showed single nucleotide polymorphisms, several of which resulted in amino acid substitutions : NEUROD1, Ala45Thr; PAX4, Pro321His and Pro334Ala. These amino acid sequence variants were not associated with Type II diabetes. Conclusion/interpretation. Our results indicate that NEUROD1 and PAX4 are not a common cause of either MODY or late-onset Type II diabetes in the French Caucasian population. [Diabetologia (1999) 42: 480–484]