A sensitive and rapid method for analysis of phosacetim in rabbit tissues and blood has been developed. It requires extraction from biological materials followed by TLC. The assay allows good reproducibility, high recoveries (about 80%), excellent linearity in the range of 0.1 to 20 micrograms with r equal to 0.999, and a low detection limit, 0.05 microgram. The results from TLC were in conformity with those from HPLC. In addition, the assay was applied to study the distribution of phosacetim in rabbit tissues.