Very little is known about the normal temporal and quantitative relationships between gastric emptying and gall bladder emptying. Using a non-invasive double isotope technique these relationships were investigated in 22 normal healthy adults. 99Tcm EHIDA was used as the biliary tracer and 113Inm labelled bran as the gastric content tracer. Gastric emptying was monoexponential with a t1/2 of 45 +/- 3 minutes (mean +/- SEM). In 15 subjects the gall bladder emptied in relation to eating according to a double exponential function. In these subjects 15.0 +/- 1.6% of gall bladder contents emptied before gastric emptying began. They could be further divided into two clear cut types (p less than 0.001), according to the ejection fraction at 10 minutes and the t1/2 of the first exponential. Emptying of the gall bladder was faster and more of its contents were ejected in subjects with a type I response (n = 9) than in subjects with a type II response (n = 6). In the remaining seven subjects the gall bladder began to empty spontaneously, unrelated to eating. These observations suggest that gall bladder emptying: (a) may have a cephalic phase, (b) can be expressed as a double exponential function, (c) may occur unrelated to eating, (d) which occurs only in relation to eating would appear to be either fast (type I) or slow (type II).