Gulf and Marshall ryegrass (Lolium multiflorum) accumulate relatively high concentrations of phosphorus (P) in their shoots. In order to evaluate their potential to utilize organic P substrates, seedlings were grown aseptically in agar-nutrient medium enriched with 0-20 mM myo-inositol hexaphosphoric acid for 5 weeks, and patterns of growth, P accumulation, root phosphatase activities were studied. Plants registered a differential growth pattern, Gulf ryegrass showing greater increase in biomass than Marshall ryegrass. Shoot accumulation of P was dependent on the concentration of the substrate present in the nutrient medium and reached up to 1% (dry weight). Activities of phytase in root extracts of P-enriched plants were about two fold higher than the control (in the absence of P). Activities of root phosphomonoesterase were up to 45% and 62% higher than controls in Gulf and Marshall ryegrass, respectively.