Post HIV-1 entry, productive HIV-1 infection of primary T cells requires overcoming several cellular blocks to provirus establishment and replication. Activation of unknown host intracellular events overcomes such inhibitory steps and is concomitant with HIV-1 replication. We show that the transcription factor NFATc was sufficient as a cellular factor to induce a highly permissive state for HIV-1 replication in primary CD4+ T cells. NFATc overcame a blockade at reverse transcription and permitted active HIV-1 replication. Pharmacologic blockade of endogenous NFAT activity by FK506 or CsA inhibited synthesis of reverse transcription and also potently blocked HIV-1 replication. T cells therefore can become competent for HIV-1 replication by control of regulated host factors such as the NFATc transcription factor. The host mechanisms regulated by such permissivity factors are potential targets for anti-HIV-1 therapy.