Abstract 1. 1. After 0.1 mM 1-naphthol was injected into intestinal loops, 70–90% of the 1-naphthol in the intestinal venous blood was present as 1-naphthol glucuronide. For 1.0 and 2.0 mM injections the proportion of 1-naphthol present as 1-naphthol glucuronide was 25–50%. 2. 2. The proportion of 1-naphthol glucuronide in the intestinal venous blood was increased by oral dosing of either sodium phenobarbital or 3,4-benzpyrene but these compounds did not alter the rate of appearance of 1-naphthol, free or conjugated.