The benefits and optimal applications of chemotherapy in the management of retinoblastoma remain to be defined. There are major obstacles to its further study in the clinical setting. A xenograft model of human retinoblastoma heterotransplanted directly into the anterior chamber of the nude mouse eye has been adapted for evaluation of therapeutic efficacy. Cyclophosphamide, the most effective conventional drug, and diaziquone, an experimental agent, both produced documented and comparable responses in each of four xenograft cell lines. There was no evidence of rapidly emerging drug resistance or cross-resistance between the two agents when sequential chemotherapy courses were given. Diaziquone is an effective chemotherapeutic agent for retinoblastoma in the xenograft model, and may have applications in clinical management.