The sensitivity and specificity of ultrasound-directed fine-needle biopsy in the differentiation of malignancy or otherwise of structures in the abdomen or retroperitoneal space which look suspicious on ultrasound was evaluated from results in 558 patients (306 men, 252 women). Data from two different centres were used to characterize further the influence of different techniques of puncture, cytopathologists and groups of patients on the validity of the examination. Sensitivity (in the two centres) was 88 and 80%, respectively, specificity 100 and 99%. The validity of the examination was the same at both centres. In both centres the sensitivity was worst for pancreatic tissue, at only 72 and 61% respectively, compared with other organs (e.g. liver, lymph nodes, kidney) (P less than 0.05). Fine-needle biopsy of abdominal and retroperitoneal organs will thus be subject to a not insignificant number of false-negative results of cytological examination.