The effect of magnesium and iron on the growth, cellular morphology, deoxyribonuclease, coagulase, and enterotoxin B (SEB) production of Staphylococcus aureus strain S-6 in a pancreatic digest of casein (NAK) which had been treated with alumina to remove mineral ions was determined. Growth of S. aureus in the treated NAK medium (NAKSA) was minimal; the morphology of the cells was heterogenous with many large cells as well as some that were gram negative. The cells gradually reverted towards normal as the Mg2+ concentration was increased to 1.1 μg/ml. Cell dry weight increased from 0.36 ± 0.27 mg/ml to 1.16 ± 0.41 mg/ml, DNase activity increased from 7.6 units/mg dry weight to 77.0 units/mg dry weight, and SEB production increased from 12.2 to 54.3 μg/mg cell dry weight when the Mg2+ content was increased to 1.1 μg/ml. Increasing the Fe2+ content above the 0.4 μg/ml in the NAKSA medium containing 1.1 μg/Mg2+ resulted in decreases in dry weight and DNase activity, a slight increase in SEB production, and a relatively large increase in coagulase production.