Urinary oxalate concentrations were measured in 45 patients with quiescent Crohn's disease, four patients with chronic pancreatitis and five healthy subjects after a normal oxalate (150 g/day) diet, after a high-fat (150 g/day), normal oxalate diet and after and after a high-oxalate (500 mg/day) diet. Urinary oxalate concentrations were significantly (P less than 0.05) higher in patients with Crohn's disease and steatorrhoea, but not in those with chronic pancreatitis, after administrating a high-oxalate diet compared with healthy subjects. Mean oxalate values were 19.1 mg/24 h in controls compared with 65.8 mg/24 h in Crohn's disease patients. A direct correlation (r = 0.37, P less than 0.01) was established between faecal rats and urinary oxalate after oval oxalate load: this correlation (r = 0.43, P less than 0.01) is closer when only patients with Crohn's disease are considered. The study, therefore, confirmed a correlation between steatorrhoea and hyperoxaluria in patients with Crohn's disease; however, the high percentage of false positive results limits the use of urinary oxalate concentrations as a reliable indicator of lipid malabsorption. It is concluded that, at present, measurement of urinary oxalate cannot be recommended as a valid alternative to the Van de Kamer method for diagnosing lipid malabsorption.