A gastric delivery system (GDS) for iron supplementation was evaluated. Radioisotopic studies in 9 volunteers demonstrated a three-fold higher absorption of GDS iron compared with ferrous sulphate elixir. A double-blind placebo controlled trial was done in 200 women to compare the gastrointestinal side-effects associated with 50 mg iron daily given either as GDS or conventional ferrous sulphate. The conventional preparation was associated with a significantly higher frequency of nausea and anorexia, whereas there were no significant differences in reported side-effects between subjects receiving GDS or placebo. A single GDS capsule daily provides the same amount of absorbed iron as conventional ferrous sulphate given three times daily, and does not produce gastrointestinal side-effects.