Different effects of thymidine and 5-fluorouracil 2'-deoxyriboside on biosynthetic events in cultured P815Y mast cells.

1. Addition of 2mm-thymidine, although resulting in the cessation of cell division, allows the continuation of phospholipid and protein synthesis and results in an increase in mean cell volume for at least 15h. 2. 5-Fluorouracil 2'-deoxyriboside inhibits cell division but differs from thymidine by inhibiting the synthesis of phospholipid and protein in a more marked manner. 3. The relation between these results and the P815Y cell cycle is discussed.