We studied carnitine absorption in rats rendered azotemic by subtotal nephrectomy (RF) and compared the results with those obtained in a sham-operated group on liberal food intake (NL) and those pair-fed (PF) with the RF group. Animals with short-term (2 weeks post-nephrectomy) and long-term (5-6 weeks post-nephrectomy) RF were studied. In vivo recirculating perfusion was used. A significant reduction in carnitine absorption (expressed per unit length) was noted in the short-term RF and PF groups when compared to the NL controls. When the data were corrected for intestine weight, the short-term RF and PF groups showed comparable absorption rates with the NL group. These findings suggest that in animals with short-term RF, weight loss is responsible for the observed alteration in carnitine absorption. Intestinal segments from PF and short-term RF animals had significantly greater carnitine accumulation suggesting decreased release into the circulation. In the long-term RF setting, RF and PF animals demonstrated reduced carnitine absorption. When the data were expressed per unit of weight the absorption rates normalized, implicating reduced intestinal mass as the factor responsible for reduced carnitine absorption. No significant difference was found in the amount of residual carnitine suggesting amelioration of impaired transport out of the enterocyte in chronic RF.