Ninety patients with inoperable carcinoma in the terminal stages and 12 patients in serious condition with other tumor types were given benzaldehyde in the form of beta-cyclodextrin benzaldehyde inclusion compound (CDBA) orally or rectally at a daily dose of 10 mg/kg divided in four doses. Toxic effects, including hematologic or biochemical disturbances, were not seen during long-term successive administration of CDBA. Fifty-seven of the patients treated were evaluable; 19 patients responded completely and ten patients responded partially (greater than 50% regression). For all responding patients longer response durations were associated with longer CDBA treatment periods. Treatment of squamous cell carcinoma induced the cancer cells to change into a conglomeration of pearls (the well-known product of differentiation) which consisted of keratinized normal squamous cells.