Community studies from Guinea-Bissau have found that 30-40% of HIV-2-infected individuals' spouses are also infected. However, wives aged under 25 years were significantly less likely to be HIV-2-seropositive. A study was conducted to examine whether proviral load is important for HIV transmission between spouses. Proviral load was examined in 121 HIV-2-infected adults in a rural area of Guinea-Bissau. For the 68 subjects with a spouse of known HIV status, the risk of the spouse being infected was studied. Statistical methods were used for dependent data since several couples were polygamous. 27 HIV-2-infected men had 52 current wives of whom 17% were HIV-2-seropositive. 41 HIV-2-infected women had 36 current husbands of known HIV serostatus; 9 were HIV-2-seropositive. Univariate analysis found the concordance of female partners of HIV-2-infected men to increase with a previous history of prostitution, age of wife, lack of age difference between the spouses, number of previous husbands, the number of wives of the man, and the proviral load. The only significant predictor of concordance in multivariate analysis when wives with a history of prostitution were excluded was being of age 45 years or older. That tendency was not explained by the length of current marriage. Among spouses of HIV-2-infected women, none of the examined factors predicted whether the husband was HIV-2 infected. It was concluded that women seem to be more susceptible to HIV-2 infection after age 40-45 years. That change in susceptibility may be a major reason for the distinctive age pattern of HIV-2 infection observed in West Africa.