Perennial ryegrass (S23), timothy (S48), white clover (S100) and red clover (Hungaropoly), grown in culture solutions containing 0.2 × 10−7, 1.0 × 10−7, 5.0 × 10−7 and 1.0 × 10−6M-potassium iodide, showed relatively small differences in iodine uptake. The lowest uptake occurred with timothy, the species that also produced the lowest yields of dry matter