A conventional diet fed to rats in an agar-gel base reduced mature body weight by about 25% and increased longevity when compared to the same diet in pelleted form. Dry matter intake was not affected, but food utilization was considerably poorer. The use of a diet in agar gel may, therefore, provide an improved toxicological assay, especially when used in combination with flushing racks housing 2 animals per cage, where exposure of the animal technician to dust was reduced.