In former investigations our group obtained an immuno-reconstituting effect in mice treated by immunosuppression after a continuous treatment with splenopentin (SP5). The goal of the present study was to test whether a small number of injections right after immunosuppression possibly produces the same result in the sense of an initial effect. Although a short-term therapy induced an increase of antibody formation which was measurable after 4 weeks, the study clearly showed that only a continuous treatment by SP5 led to an optimum, i.e. complete reconstitution of antibody formation.