A comparison of the activity against human immunodeficiency virus 1 of zidovudine (AZT) and poly I poly C double-stranded RNA both alone and in combination in MT4 cells and primary monocyte/macrophage (M/M) cultures was made. The inhibition of the HIV-induced cytopathic effect or reverse transcriptase production by AZT in MT4 cells was not modified by the combination of the two agents. In contrast, AZT inhibition of reverse transcriptase production in the supernatant of M/M cultures was enhanced by the addition of poly I poly C. The inhibitory effect of the drug combination was more marked in M/M than in MT4 cells, indicating that the evaluation of compounds involving the induction of an antiviral state should be tested not only CD4+ T cells but also in monocyte-macrophages.