The clinical effects of irradiation on the oral mucous membrane of 22 patients with oral or circumoral carcinomas (oral group) were compared with nine patients with laryngeal carcinomas (laryngeal group). Each of the patients received 6000 rads of radiation in divided doses five days each week for five weeks, alternately left and right sides. After one week of irradiation, patients in the oral group had diminished salivary flow, some erythema and orally-derived pain. After three weeks, severe clinical changes were present and these changes increased throughout the treatment period. Four to six months after treatment, the majority of the clinical changes had resolved in the oral group but salivary flow from parotid and submandibular/sublingual glands was still diminished. The laryngeal group had few clinically detectable oral changes at any time, with the exception of diminished salivary flow which recovered four to six months later in the case of the parotid glands but not in the submandibular and sublingual glands. The fungal flora changes in these two groups of patients are fully described elsewhere. Both oral and laryngeal groups had similar sharp rises of fungal colony counts with little diminuation even at six months after treatment, despite the abatement of signs and symptoms. It is suggested that direct radiation damage is the primary cause of oral symptoms with the role, if any, of fungi being that of opportunist pathogens on compromised tissues.