The hypervariable region 5' to the human insulin gene has been characterised in two South African Indian families, each having two generations of individuals affected with non-insulin-dependent diabetes mellitus (NIDDM). Southern blot analysis, with the restriction endonuclease Pvu II and plasmid phins 310 as a probe, was used. In family 1, class 1 alleles (0.87, 0.79, 0.72 and 0.68 kilobase (kb)) were found at this locus but no linkage with NIDDM was shown. In family 2 a class 3 (2.51 kb) and two class 1 alleles (0.89, 0.76) were found. The 0.89 kb allele appears to be segregating with NIDDM in this family.