Calcium bioavailability of vegetarian diets containing various proportions of candidate crops for a controlled ecological life-support system (CELSS) was determined by femur 45Ca uptake. Three vegetarian diets and a control diet were labeled extrinsically with 45Ca and fed to 5-wk old male rats. A fifth group of rats fed an unlabeled control diet received an intraperitoneal (IP) injection of 45Ca. There was no significant difference in mean calcium absorption of vegetarian diets (90.80 ± 5.23%) and control diet (87.85 ± 5.25%) when calculated as the percent of an IP dose. The amounts of phytate, oxalate, and dietary fiber in the diets did not affect calcium absorption.