1. A ninhydrin-reacting substance seen during ion-exchange chromatography of faecal dialysate obtained in vivo from normal and uraemic subjects has been isolated and identified as methylamine.
2. Faecal dialysate concentrations of methylamine were higher in uraemic subjects and were related to the degree of renal impairment (P < 0·05).
3. Methylamine concentrations in faecal dialysate and centrifugate were not significantly different.