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I would agree that this is of little value in semi-solid or solid stools. we had one memorable case of profuse waterly diarrhoea in a young child that turned out to be a Munchausen by proxy (Meadow's syndrome) where a mother was giving her child magnesium sulphate. Analysis of spun supernatant showed an "osmolar gap" with a marked discrepancy between measured and expected osmolality (based on measuremnet of faecal sodium. potassium and chloride). This encouraged us to look further and the finding of a high magnesium (and subsequently sulphate) concentration empowered the paediatricians to confront the mother. so there may be rare situations where the lab has a part to play in the analysis of diarrhoea but the clinicians have to make a good case! (never say "never" in medicine?) James Falconer Smith %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%