Abstract
A new liquid medium, with fetal calf serum as the sole undefined component, was devised for the cultivation of Trypanosoma cruzi. The need for the serum is ascribed to its mitogenic proteins, which stimulate division of, and the uptake of [3-H-] thymidine by the parasites. In the new medium, T. cruzi has a cycle culminating in the apperance of up to 90 per cent metacyclic forms in the stationary phase. This cycle is repeated on each serial transfer.