Pneumocystis carinii pneumonia is a major complication of T-lymphocyte immune deficiency. Restriction of the disease to the alveolar spaces and failure to culture P. carinii has hindered simple diagnostic methods. We have developed a specific DNA amplification method for P. carinii and shown diagnostic sensitivity and specificity exceeding 95% for pneumocystis pneumonia when applied to bronchoscopic lavage and hypertonic saline induced sputum. We here report application of DNA amplification to simple oropharyngeal samples in 31 HIV-positive patients with respiratory illness. P.carinii-specific DNA was detected in 10 of 18 (56%) patients with pneumocystis pneumonia by ethidium bromide stained gels and 14 of 18 (78%) patients by the more sensitive technique of oligoblotting. P.carinii DNA was not detected in samples from 13 patients with other respiratory diagnoses. An oropharyngeal sample offers a simple specimen for detecting P.carinii by DNA amplification; refinements of technique and calibration may allow its development for accurate diagnostic and epidemiological work. © 1993 Oxford University Press.