This study evaluates, for the first time by direct visualization, the microvascular distribution of microspheres in normal hamster cheek pouch and in hamster cheek pouch bearing tumor induced by 7, 12 Dimethylbenz (A) Anthracene solution (DMBA). In contrast to the results of the previously used open-chest technique, this carotid injection technique does not lead to irregular distribution of 15-mu carbonized microspheres, chain, or impaction phenomena. It is concluded that methodology differences may account for different results.