Forty-eight patients with urinary bladder neoplasms were examined with magnetic resonance imaging before and after intravenous administration of gadolinium diethylene-triaminepentaacetic acid (DTPA). Spin-echo sequences with short repetition and echo times were used in all patients; in 20 a gradient-echo technique was used to perform sequential imaging. In 31 patients ratios of tumor signal intensity to that of fat, muscle, and bone marrow were calculated before and after Gd-DTPA enhancement on T1-weighted spin-echo images. Increases in tumor signal intensity on T1-weighted spin-echo images were statistically significant after contrast enhancement (alpha = 1%, P less than .0001). The average rise in relative signal intensity after contrast enhancement was 120% for the tumor-fat ratio (tumor-marrow ratio, 105%; tumor-muscle ratio, 85%). Tumor signal intensity peaked within 120 seconds and remained on a plateau for up to 45 minutes. Necrotic tissue within the tumor, seen in three cases, was detectable only on contrast-enhanced images.