The relationship between asymptomatic human immunodeficiency virus (HIV) infection and blood hemoglobin (Hb) concentration was examined in anemic pregnant women from a population with high prevalence of both anemia (60%) and HIV seropositivity (30%). Sera from 155 pregnant women with Hb levels < 10.5 g/dL were tested for HIV status, C-reactive protein (CRP), vitamin B12, retinol, and folate levels. The observed prevalence of HIV seropositivity in the group of women with anemia was 47.1% (95% confidence interval=39.2-55.0%). This is significantly higher than the HIV prevalence in the whole population (30.1%; P < 0.001). Median Hb values in HIV-seropositive and -seronegative women with anemia were 8.40 g/dL and 8.95 g/dL, respectively. Serum retinol, vitamin B12, and folate levels were not significantly different in the HIV-seropositive and -seronegative groups. In women who were HIV-seropositive with normal levels of CRP, a median decrease in Hb of 0.4 g/dL was observed. For those with serum CRP levels > 25 mg/l, the median decrease in Hb was 0.7 g/dL. Results indicate that asymptomatic HIV infection is associated with increased prevalence and severity of anemia in pregnancy in this population.