Agglutination by concanavalin A of normal chick embryo fibroblasts treated by 5‐bromodeoxyuridine (BrdU)

When chick embryo fibroblasts are grown for two days in the presence of low doses (18 μg/ml) of 5‐bromodeoxyuridine (BrdU), their agglu‐tinability by Concanavalin A is increased to about the same degree as following viral transformation of the cells by Rous sarcoma virus. Simultaneous addition of a large excess, but not of a low dose of thymidine prevents this effect of BrdU. Treatment with BrdU also enhances the agglutinability of fibroblasts infected with a conditional It mutant of Rcus sarcoma virus at the temperature of 41° which restricts morphological transformation.