Fatal susceptibility to cycloheximide of mice bearing Ehrlich ascites tumours and of animals pretreated with cell-free Ehrlich ascites tumour fluid.

Soluble, but unidentified, factors in cell-free Ehrlich ascites tumour fluid induced, after a delay period, a fatal heparin- and ancrod-resistant susceptibility to a normally tolerated dose of cycloheximide. The evidence suggests that production of such factors is dependent upon interaction of tumour cells with the intravascular or the intraperitoneal compartment. The factors are considered likely also to play a crucial role in the similar heparin and ancrod-resistant fatalities which follow cycloheximide challenge of mice bearing established Ehrlich ascites tumours and in the deaths of mice challenged with cycloheximide 24 h after an intravenous injection of washed Ehrlich ascites tumour cells. These factors play no part in the heparin- and ancrod-preventable fatal syndrome following cycloheximide challenge either 2 h before or 2 h after intravenous injection of washed Ehrlich ascites tumour cells.