Naturally occurring Eaton PPLO was shown to propagate on an agaryeast extract-horse serum medium. The agent was recovered directly on agar from 12 of 13 serologically positive patients with pneumonia. Eaton PPLO was not recovered from 14 serologically negative pneumonia patients. All Eaton PPLO isolates produced small homogenously granular colonies which could be easily differentiated from the usual “fried egg” or “nippled” colonies produced by non-Eaton oral PPLO. The distinctive colonial morphology of Eaton PPLO may ultimately prove useful for its presumptive identification.