The aim of this study is to determine the effect of anticholinergic therapy on the gastrocolonic response to a standard meal or its major constituent fat. A rapid increase in rectosigmoidal spike activity occurs after ingesting the standard meal or the fat meal (P less than 0.01). Distal colonic motility returns to fasting levels 50 min after both meals. There is no further increase in spike activity after the 1000-calorie meal, but spike activity increases again 70 min after ingesting the fat (P less than 0.02). The anticholinergic drug, clidinium bromide, inhibits the early increase in spike activity after both meals. However, the anticholinergic has no effect on the delayed peak of activity following the ingestion of fat. This study suggests that (a) the early gastrocolic response to a standard meal and a fat meal is cholinergically mediated and (b) the late increase in rectosigmoidal motility occurs only after fat ingestion and may be controlled by other neural mediators or possibly the gastrointestinal hormones.