Human lymphocyte colonies were grown in semi-solid culture in the presence of staphylococcal protein A. The best results were obtained when 1 × 106 lymphocytes were cultured for 5 to 7 days with 25 to 50 µg of protein A per dish. A lineal relationship was observed between the number of cells seeded and the number of colonies developed. An increased number of colonies was seen in cord blood culture compared with that in child and adult peripheral blood. The addition of 5 × 10-5 M of 2-ME to the culture approximately doubled the colony counts. The cells harvested from the colonies contained about 70% of E-RFC and 20% of EAC-RFC.