Lung primary carcinomas and normal tissue from 136 patients have been extracted for prostaglandins, and the findings examined in relation to histology. In most cases, tumours yielded more prostaglandin-like material (PG-lm), as judged by bioassay, than did normal tissue from the same lungs. Amounts varied with tumour types, in the following ascending order: small-cell carcinomas, large-cell undifferentiated carcinomas, well-differentiated squamous carcinomas, poorly-differentiated adenocarcinomas, poorly differentiated squamous carcinomas, and well-differentiated adenocarcinomas. Tumour PG-lm was highest when necrosis or the neutrophil content of the tumours were moderate, whereas PG-lm from normal lung tissue correlated with the number of macrophages. Chromatography indicated the presence of various prostaglandins, in agreement with our recent findings using gas chromatography--mass spectrometry.