The effect of HIV-1 infection on cytokine levels was studied in monocytic cells by using Northern blotting analysis. Monoblasts (THP-1, U937) did not express IL-1 beta RNA even if the cells were infected with HIV-1. After exposure to LPS (10 micrograms/ml) and 12-O-tetradecanoylphorbol-13-acetate (TPA, 100 nM) for 12 h, these HIV-1-infected monoblasts accumulated 8-15-fold greater levels of IL-1 beta RNA as compared with their HIV-1-uninfected counterparts that were similarly stimulated. In contrast, levels of RNAs coding for monocyte-colony-stimulating factor (M-CSF) and tumor necrosis factor-alpha (TNF alpha) were elevated less than twofold in the HIV-1-infected cells as compared with HIV-1-uninfected cells after their stimulation with LPS and TPA. Inhibition of new protein synthesis did not block the marked accumulation of IL-1 beta RNA produced by exposure to LPS and TPA in the HIV-1-infected cells. Time-course experiments showed that the maximal levels of IL-1 beta RNA occurred at 12 and 24 h after LPS and TPA stimulation of the HIV-1-infected and uninfected U937 cells, respectively. Studies of stability of RNA using actinomycin D showed that IL-1 beta RNA was equally stable in infected and uninfected U937 cells after their stimulation with TPA and LPS. Taken together, our data show that HIV-1 infection markedly augments IL-1 beta RNA accumulation in stimulated monocytic cells, probably through increasing rate of transcription of IL-1 beta.