1. The effect of drugs that cause neutropenia has been tested upon normal bone marrow colony formation in semi-solid agar.
2. Thiouracil, methimazole and phenylbutazone do not cause inhibition whereas sodium aurothiomalate, 6-mercaptopurine and chloramphenicol cause dose-related inhibition of colony formation at or below drug concentrations found in serum during therapy. Chloramphenicol also inhibits mouse bone marrow, L cells and Hela cells in agar culture.
3. Dose—response curves have been analysed by the probit method and found to be reproducible.