Aspects of chalone action.

The following aspects of action of a chalone-like factor for the Ehrlich ascites mammary carcinoma and of the granulocytic chalone are discussed: 1) Dependence on the state of proliferation. Rapidly growing cells respond poorly or not at all. 2) Antagonism with growth factors. The factor for the Ehrlich ascites mammary carcinoma is antagonized by physiological concentrations of insulin or by proinsulin. The granulocytic chalone is antagonized by colony stimulating factor. 3) Influence on cell cycle progression. Attempts and problems to analyse this influence for the factor for the Ehrlich ascites mammary carcinoma by flow cytometry are described.