In a blind sequential trial, 16 healthy volunteers were given glyceryl trinitrate tablets in 300/tg or 500/tg dosage, both sublingually and by chewing, at two separate sessions. Plasma GTN levels were estimated and, in addition, each subject was monitored in regard to pulse, blood pressure and peripheral blood flow.Results showed a higher overall plasma GTN level following 500/tg, but no enhancement of absorption rate responses as compared to 300/tg. Chewing increased the absorption rate at 300/tg, but not at 500/tg and the pulse rate was marginally higher from chewing at both doses.It is suggested that, for the prophylaxis of angina pectoris, tab GTN 300/tg be placed under the tongue. In the presence of anginal pain, it should be chewed briskly and the dosage increased only when proved necessary.