Forty-four patients with unresectable primary, residual, or recurrent colorectal carcinoma confined to the pelvis were randomized to treatment with split course megavoltage radiotherapy alone (5,000 rad given over 7 weeks) or in combination with the intradermal administration of the methanol extraction residue of BCG (MER) over an eight-month period. No improvement was observed in frequency of symptomatic palliation, interval to progression, or survival among patients receiving MER. Furthermore, there was no evidence of enhanced immunological status in patients receiving MER as compared to those receiving radiation alone. Although temporary pain relief was seen in 94% of patients with pretreatment pelvic or perineal pain, 37 patients (84%) have experienced subsequent progressive malignant disease. Regional recurrences within the radiotherapy port were observed in 28 of 31 patients who were evaluable for analysis of pattern of sites of initial progression. Eleven of the 28 patients with local failure also had distant metastasis at the time of tumor progression. There was no discernible clinical value associated with MER treatment in combination with radiotherapy as employed in this study. The high frequency of pelvic recurrence following radiotherapy at the dose and schedule we employed highlights the need for more effective treatment strategies for this group of patients.