1) With animals of 100 gm. the DL50 for caffeine sodium benzoate is 1.0 g./kg. in the female of Bufo arenarum Hensel, and 0.9 g./kg. for the male at 24°C.
2) If a given dose per unit weight is injected, mortality is higher with large animals than it is with the small ones.
3) This difference disappears when the drug is injected according to the following formula: D = K. Wn, obtaining then a mortality quite uniform, when the exponent n is 0.75.
4) The relatively smaller metabolism of the larger animals can be compensated by keeping them in a higher temperature.
5) There is a close relation between the intensity of metabolism and the processes of detoxication of caffeine.
6) The application of the procedure under study to other drugs and species is discussed.