Gastrointestinal transit in the chicken was investigated by using 198Au-colloid as a marker. Gastrointestinal transit was determined following administration of a 198Au-colloid solution (370 kBq (10 microCi), 0.5 ml) into the proventriculus by measuring the distribution of radioactivity in the gastrointestine. Most of 198Au-colloid administered into the proventriculus was transferred instantly to the gizzard and subsequently, some part of it quickly to the duodenum and the upper segment of the jejunoileum. A considerable quantity of 198Au-colloid in the duodenum, the upper and middle segment of the jejunoileum regurgitated to the gizzard. 198Au-colloid transferred to the caecum was retained for a long time (more than 48 hours) in these segments. A part of 198Au-colloid was found in the feces 90 to 120 minutes after administration into the proventriculus and the greater part of it was excreted into the feces 24 to 48 hours. Subcutaneous administration of acetylcholine (2 mg/kg) increased the gastrointestinal transit but atropine (2 mg/kg) decreased.