A method for the detection of Streptococcus pneumoniae in sputum samples by PCR has been developed. The assay employs oligonucleotide primers specific for a portion of the autolysin gene lytA of S. pneumoniae. Other closely related streptococci, Haemophilus influenzae, and Moraxella catarrhalis do not give a positive result in the assay. The assay was capable of detecting between 10 and 100 CFU of S. pneumoniae in distilled water and 1.4 x 10(4) CFU/ml in simulated sputum samples. Sputum samples from 33 patients with acute pneumonia were collected and subjected to culture, PCR, and C-polysaccharide antigen detection by enzyme-linked immunosorbent assay (ELISA). A significant isolate of S. pneumoniae was isolated from 14 patients, of which 13 were positive by PCR and C-polysaccharide antigen ELISA. No positive results were obtained for the 19 patients in whom other pathogens or upper respiratory tract floras only were isolated. The sensitivity of the autolysin PCR is 92.8%, the specificity is 100%, the predictive value of a positive result is 100%, and the predictive value of a negative result is 95%. This suggests that autolysin PCR is suitable for the detection of S. pneumoniae in clinical samples.