ABSTRACTConcentrations of cellular fatty acids, proteins and nitrogen and activities of phosphatases were measured in mycelia ofEndogone pisiformisgrown in liquid culture for 4, 7, 14 and 25 days. All of these parameters varied with culture age. Concentrations of total fatty acids and soluble proteins were highest at 4 days of growth (early log phase) and decreased at 7, 14 and 25 days. Nitrogen concentration increased only at 25 days of growth. The activities of phosphatases varied significantly with the pH of the enzyme and with culture age. Alkaline phosphatase activity significantly increased to a maximum at 7 days of growth (late log phase) and progressively decreased thereafter, while the activity of acid phosphatase remained unaltered at all times. The protein pattern obtained from a one-dimensional electrophoretic gel revealed the presence of five major bands at 41.5, 35.5, 21.5, 18.5, 17.2 and 12.8 kD, the position of which did not vary with culture age. The concentrations of fatty acids 16:0, 18:0, 18:1, 18:3 (Δ6,9,12) and 19:0 varied significantly in different lipid classes and with days of growth. The occurrence of both isomers of linolenic acid (18:3Δ6,9,12and 18:3Δ6,9,12) in mycelia ofE. pisiformisis the third report of their common co-occurrence in members of the Endogonaceae.