  This paper deals with a skew-normal model of the relation between a dose $d >
0$ and a quantitative measure $E(d)$ of an effect of the administered drug.
Precisely, $E(d)$ is a measure of the therapeutic response or a measure of a
side-effect. Some existing and additional properties of the logistic functions
are proved, and a skew-normal model of the escape time of rats under an
experimental antidepressant medication is provided.
