Hyperoxaluria was documented in patients with pancreatic insufficiency, adult celiac disease, regional enteritis after ileectomy and partial colectomy, and jejunoileal bypass. The degree of hyperoxaluria correlated directly with the severity of the steatorrhea and inversely with the dietary calcium content. High-calcium diets suppressed oxalate excretion to normal when fecal fat excretion was approximately 30 g/day or less. In patients with more severe steatorrhea, decreasing dietary fat and oxalate content further reduced urinary oxalate excretion. These data suggest that, while steatorrhea is the most important determinant for enhanced absorption of dietary oxalate, variations in dietary calcium content modulate the amount of oxalate absorbed.