Two patients with malignant insulinoma and hepatic metastases were treated with streptozotocin, administered directly into the celiac artery. Decreases in tumor size were documented radiographically. One patient was in a terminal state when first treated, but the other patient was in moderately good general health and responded well. Some side-effects, including renal tubular damage, were observed but were relatively minor. Streptozotocin therapy offers some benefit in patients with malignant insulinoma.