Grain's stain (GS) and culture of sputum are used routinely for diagnosis of lung infection. We prospectively studied physicians' use of sputum GS and culture for management of lung infection, the correlation between GS and culture in 224 adequate sputum specimens from patients admitted to our hospital over a 15-month period, and its impact on the antibiotic used. GS correlated with sputum culture in one third of the cases in the most predictive group. Gram-negative rods including Haemophilus influenzae formed the majority of the positive cultures and were also the most poorly predicted by GS. Physicians used broad spectrum antibiotics empirically in most cases. These choices were not altered by the culture results in most instances. It may be reasonable to use broad spectrum antibiotics empirically for lung infection. Sputum GS and culture may be helpful in patients at risk for high morbidity and mortality.