The relationship between immunoglobulin allotypes and leprosy was studied in 91 unrelated patients and 100 healthy controls from Vietnam. Twenty Vietnamese patients with tuberculosis were also typed for the Gm, A2m and Km allotypes. The results were compared with those from the healthy controls. No significant association was found for the allotypes G1m(z,a,x,f) G2m(n), G3m(g,b), A2m(1,2) and Km(1,3) between the two groups of patients and the controls. Heterogeneity in the distribution of G2m(n), G3m(b), A2m(2) and Km(3) was found when 60 polar-lepromatous (LL) patients and 27 borderline-tuberculoid (BT) patients were separated out of the 91 leprosy patients. In the LL patients there appeared to be a significantly higher frequency of G2m(n), G3m(b) and A2m(2) in comparison with the BT patients (P less than 0.05). A significantly lower frequency of Km(3) was found in the LL patients in comparison with the healthy control group (P less than 0.05). The frequencies of the Gm-A2m haplotypes and of the occurrence of the Km(1) and Km(3) in the Vietnamese population were calculated on the basis of the results in the 100 samples of healthy controls. The main haplotype is Gmaf;n;b (frequency 0.676), occurring with A2m1 (0.200), as well as with A2m2 (0.476).