Abstract/Text: Ninety-six sputum specimens from patiens with pneumonia were microscopically screened for leukocytes and buccal squamous epithelial (BSE) cells. Cultures of these specimens were compared with cultures of paired transtracheal aspirates (TTA). Agreement between sputa with less than 25 BSE cells per 100X field and TTA was good (79%). Only 27% of the specimens with greater than 25 BSE cells per 100X field agreed with TTA. Sixty-six of the sputa were of group 5 quality, i.e., greater than 25 leukocytes and less than 10 BSE cells per 100X field. A potential pathogen growing in one of these specimens was 94% predictive of growth in the TTA. If a group 5 sputum was negative for a potential pathogen, there was a 45% chance that a fastidious organism had been overgrown or overlooked. The presence of definite lower tract secretions in group 5 sputa as determined by visualizing bronchial epithelial cells and alveolar macrophages did not significantly increase the diagnostic value of these specimens. Microscopic screening of sputum before culture with rejection of selected specimens can increase the value of sputum in determining the etiology of bacterial pneumonia.