Nonspecific acid α-naphthyl esterase (ANAE) activity was tested in splenic white cells from thymectomized and sham-thymectomized larvae ofBufo bufoto individualize T-lymphocytes. By ANAE technique T-lymphocytes ofBufodisplay a characteristic red brown reaction (T-pattern) and are readily distinguished. Thymectomy was performed at two different larval stages. The total number of white cells for each spleen and the number of T-pattern cells per 100 spleen white cells were determined. In addition, the number of large T-pattern cells, characterized by large spots of ANAE activity, per 100 T-pattern cells was counted. The early thymectomzied larvae exhibited a lower total number of splenic white cells. The percentages of T-pattern cells were similar in all groups. The large T-pattern cell count was lower in the two thymectomized groups, and lowest of all in the early thymectomized.