CONSIDERABLE evidence has been accumulated by Lucke1, Duryee2, Rose3, Tweedell4, and others for an agent which induces an organ-specific adenocar-cinoma in the kidney of the leopard frog, Rana pipiens. Lucke1 has postulated that this agent is probably of a viral nature. Although a percentage of the animals develop palpable renal tumours after a long and variable period of time following injection of tumour material, it is still desirable to devise other methods to propagate and possibly isolate the infective agent. At the same time, the large dimensions of the frog cells make them an ideal system with which to study the initiation of any subcellular modifications following incubation of cells with the tumour-inducing agent.