Genotypes of spring barley (Hordeum vulgare L. cvs. Alexis and Regatta) and winter barley (Hordeum vulgare L. cvs. Marina and Senate) grown under sterile and non-sterile conditions were compared with regard to the activity of root- and rhizoplane-microorganism-associated and -released phosphatases. A method is described of growing plants individually under sterile and non-sterile conditions and assaying of the enzyme activities of intact roots and rhizoplane microorganisms. The results of the experiments presented in this paper indicate that all the genotypes showed significantly (P<0.01) higher activity of extracellular phosphomonoesterase than that of phosphodiesterase both associated with and released by their roots. There were no significant differences (P<0.05) between the sterile and non-sterile root and its surrounding solutions in the activity of extracellular phosphomonoesterase. The contribution of rhizoplane microorganisms to the root total activity of extracellular phosphomonoesterase was estimated to be 3%. Generally, the activity of the enzymes associated with the roots was 20-80 times higher than the activity of those released by the roots to the surrounding nutrient solution. However, a close correlation was found between the activity of extracellular phosphomonoesterase associated with and that released by the roots.