Iopanoate saturation kinetics were measured in four dogs both drug free and following six days of low dose aspirin ingestion. Each animal acted as its own control. In post aspirin ingestion studies there was a significant (P<.001) decrease in the apparent Vmax of iopanoate. The volume of distribution showed no significant change, and gallbladder visualization showed no significant change despite the decrease in Vmax. Although aspirin pretreatment decreases the control Vmax by 50%, its mechanism and significance in the clinical setting will require further study.