The ability of dynamic, gadolinium-enhanced magnetic resonance (MR) imaging to allow prediction of histologic responses to initial chemotherapy was evaluated in 20 patients with osteosarcoma (n = 12), Ewing sarcoma (n = 4), rhabdomyosarcoma (n = 3), or synovial sarcoma (n = 1). Tumor signal intensity was measured on fast low-angle shot (FLASH) gradient-echo images obtained at 15-second intervals before and 3 or more minutes after manual intravenous injection of gadopentetate dimeglumine. Signal intensity was plotted against time, and slopes were calculated for the percentage increase in signal intensity per minute. Slopes and changes in maximum tumor size during and after chemotherapy were correlated with histologic evaluations of tumor response. Eleven of the 20 tumors met histologic criteria for response. Histologic response was moderately correlated with slopes obtained during chemotherapy (rs [Spearman rank correlation] = .53, P = .02) but not with changes in tumor size (rs = .02, P = .94). Tumor slopes obtained after chemotherapy were highly correlated with histologic findings (rs = .65, P = .007); the correlation with changes in tumor size increased but remained nonsignificant (rs = .41, P = .11).