Two areas of investigation were reviewed: (1) placebo-controlled trials of antimicrobial treatment involving patients with a clinical diagnosis of acute community-acquired bacterial sinusitis (ACABS) for whom pre- and posttherapy sinus aspirate cultures were not performed, and (2) uncontrolled trials of antimicrobial treatment involving patients with ACABS for whom pre- and posttherapy sinus aspirate cultures were performed. The clinical diagnostic criteria in the controlled trials were not correlated with sinus aspirate culture results and, thus, were of questionable validity. Most of the populations probably included patients with viral rhinosinusitis. In 10 uncontrolled studies, the posttreatment, weighted, pooled mean bacterial resolution rate (+/- standard error) at 7-10 days, based on sinus aspirate culture results, was 91%+/-10%. In 9 controlled trials, the weighted pooled mean rate of clinical improvement (+/- standard deviation) at 7-14 days for placebo recipients was 52%+/-18%. In 1 controlled trial in which diagnosis was based on duration of unimproved illness, 57% of placebo recipients and 85.5% of treated patients were healthy or had improved by day 10. Additional studies of ACABS are needed.