Filgrastim, or granulocyte colony-stimulating factor, reverses neutropenia associated with human immunodeficiency virus type 1 (HIV-1) and cytomegalovirus (CMV) infections. During a trial of anti-CMV retinitis therapies coadministered with antiretroviral therapy, 2-4 plasma specimens of HIV-1 RNA were collected from 36 HIV-1-infected patients receiving filgrastim to prevent neutropenia and from 36 patients not receiving filgrastim. For both groups, the crude mean and mean rate of change of HIV-1 log(10) RNA levels were similar. Adjustment for covariates (CD4(+) T cell lymphocytes, virus load at enrollment, level of neutropenia and antiretroviral therapy [mainly non-highly active antiretroviral therapy], and anti-CMV therapy during follow-up) resulted in a mean log(10) HIV-1 RNA level for individuals receiving filgrastim versus those not receiving the drug of 5.11 versus 4.87 (P=.12) and respective log mean rates of change per month of -0.08 versus -0.21 (P=.08). This latter difference has borderline statistical significance, which suggests that filgrastim may reduce the decline of HIV-1 RNA loads.