In 1956 our colleague, Dr. A. R. Martin,4 discovered in these laboratories that systemically administered griseofulvin produced dramatic cure in superficial mycotic infections of the guinea pig skin. It therefore became necessary to determine whether griseofulvin was safe enough to administer to man. This paper reports the investigations carried out to this end. These have already been briefly reported elsewhere (Paget and Walpole,5 1958). Methods Griseofulvin.— All the griseofulvin used in these experiments was obtained from Messrs. Glaxo as a white crystalline powder. Animals dosed orally received appropriate doses as a 4% suspension of this material in 0.5% Tween 80. The doses were given by stomach tube once daily five days a week. For parenteral, and particularly for intravenous, administration it is necessary to produce a fine-particle-size suspension. For this purpose dry griseofulvin powder was finely ground in a pestle and mortar and then suspended in 0.5% Tween