Growth‐chamber experiments on effects of light and temperature on S constituents of leaf blades, total S concentrations, and S uptake in whole soybean plants are reported. A 5‐day dark period decreased concentration of soluble protein S and increased concentrations of nonsol‐uble S, soluble nonprotein S, sulfate S, organic S, reduced nonprotein S, and total S of leaf blades. Soluble protein was decreased but S content of soluble protein was unaffected. For whole plants, dry weight and S uptake decreased and S concentration increased.