The gallbladder emptying response to sequential exogenous and endogenous cholecystokinin was measured by a noninvasive, nongeometric scintigraphic technique using a single dose of technetium 99m-labelled hepatobiliary agent. The mean latent period, ejection period, ejection fraction and ejection rate following 3 min infusion of 40 ng kg-1 of octapeptide of cholecystokinin were 2.8 +/- 0.7 min, 9.8 +/- 1.3 min, 34.0 +/- 9.9% and 3.5 +/- 2.0% per minute respectively. The corresponding values following 8 oz/70 kg of oral fatty meal were 15 +/- 6 min, 24.0 +/- 5 min (P less than 0.05), 55 +/- 9.1% and 2.8 +/- 0.6% per minute respectively. The total emptying for the combined stimuli was 71.4 +/- 14.0%. The wider range in latent and ejection period following fatty meal probably reflected the variations in time of the release into circulation and the duration of bioavailability of endogenous cholecystokinin. The lower rate of ejection was over compensated by longer duration of ejection resulting in higher degree of emptying following fatty meal. It is concluded that the gallbladder emptying pattern to exogenous and endogenous cholecystokinin can be studied sequentially using a single dose of technetium 99m-labelled hepatobiliary agent.