Radioactive phosphate was applied to the roots of intact alfalfa plants (Medicago sativa L.) on the 49th day after inoculation withCorynebacterium insidiosum (Me Culloch) Jensen and the32P contents in different fractions of phosphoric compounds were determined. In inoculated plants, susceptible to bacterial wilt, the inorganio phosphate contents (32Pinorg) was increased markedly and the32P bound in organic compounds soluble in acids (32Porg) decreased as compared with control. In roots of the same plants the32P contents in phospholipid fraction and DNA were decreased. In tolerant inoculated plants the32Pinorg increase and32Porg decrease as compared with those changes in susceptible plants were less expressive. No expressive changes in determined32P fractions have been proved in resistant plants without any visible disease symptoms.