The aim of this study was to examine serum and cellular markers of immune activation in HIV-positive (HIV+) patients with and without current opportunistic infections. Fc gamma receptor (Fc gamma R) expression on monocytes, serum neopterin and beta-2-microglobulin were studied. Thirty HIV+ patients (grouped according to Centers for Disease Control (CDC) classification) were studied and compared with 27 normal blood donor controls. HIV+ patients were further separated into three groups: 2 (CDC II), 3 (CDC III/IV without infections) and 4 (CDC III/IV with current infections). Eleven of the patients had current opportunistic infections. Results indicate that beta-microglobulin, neopterin, fc gamma RI, Fc gamma RII and Fc gamma III were significantly increased in HIV+ patients compared to controls. Further analysis of the data using Tukey-Kramer all pairwise comparison revealed that for beta-2-microglobulin the mean values for patients in groups 2, 3 and 4 were significantly different (P < 0.0001). Serum neopterin levels and the percentage of CD14+14+ monocytes expressing Fc gamma RIII showed significant differences in the mean values of group 2 and group 4; similarly, for CD4+ lymphocyte counts group 2 and group 4 were significantly different. These results indicated that beta-2-microglobulin, neopterin and CD14+ monocyte Fc gamma RIII are increased particularly in HIV+ patients with current opportunistic infections while CD4+ lymphocyte counts are reduced. The results suggest that these markers, particularly beta-2-microglobulin, could be useful indicators of the inflammatory process associated with opportunistic infection at later stages of disease where other laboratory markers may be atypical.