The efficacy of granulocyte macrophage colony-stimulating factor (GM-CSF) to enhance the immune response to hepatitis B virus vaccine has been object of several reports. We searched for randomized controlled clinical trials comparing GM-CSF given concomitantly to hepatitis B virus vaccine to vaccine given alone or with placebo. Data on rates of seroconversion (anti-HBs titers >10 IU/ml) from 13 studies (734 subjects) produced combined estimates that favored GM-CSF as compared to controls: rate ratio after a single immunization was 1.54 [95% confidence interval (CI), 1.04-2.27] and 1.20 (95% CI, 1.02-1.42) at the end of the vaccination cycle. Using a logistic approach a significant dose/response effect of GM-CSF was seen. Moreover, in renal failure patients who have responded to the vaccine, GM-CSF increased anti-HBs titers. Our findings suggest that GM-CSF induced a significant effect in terms of response rate and achievement of an earlier seroconversion to the vaccine in the overall populations examined, in renal failure patients and in healthy individuals.