THE urinary substance referred to as B in a previous communication1 has now been isolated in pure form. It can be shown to be p-phenetidine by its infra-red and ultra-violet spectra, the melting point of a picrate (176–180° C.) and lack of depression of melting point in a mixture with authentic p-phenetidine picrate (179–181° C). It is present in urine as a labile acidic substance which can be precipitated by lead acetate and purified by paper chromatography from butanol–acetic acid (R F about 0.5). The precursor seems to be a conjugate with sulphuric acid. About 2–3 per cent of administered phenacetine is excreted in this form.