Twenty-one peritoneum needle biopsies were performed in 17 patients. Proper samples for microscopic examination were obtained in 18 instances, 9 of which were diagnostic. In 6 patients with tuberculosis of the peritoneum, 5 biopsies revealed characteristic granulomas. Of 8 patients with intra-abdominal carcinoma and ascites, the biopsy in 3 revealed metastases; in 2, the diagnosis was obtained through cytologic study of the ascitic fluid; in 2 of the other 3 patients, no indication of metastases of the peritoneum was found at autopsy. The results obtained by other authors and ourselves suggest that this is a useful method which should be performed in instances of ascites of unknown etiology, suspected tuberculosis, or neoplasia.