Poly-[(trans-1,2-diaminocyclohexane) platinumj-carboxyamylose (“poly-plat“) is a second generation analog of cisplatin which enhances the immune system with greater efficacy in vitro and in vivo “Poly-plat” contains 1/5 the platinum of CDDP and demonstrates less toxicity. In order to understand the mechanism of action of this compound an in vitro and in vivo study was performed. Swiss Webster mice and isolated murine peritoneal macrophages were treated with “poly-plat” (10 mg/kg). The Swiss Webster mice were given bolus injections and sacrificed at 2 and 12 days. Peritoneal macrophages were then isolated and allowed to incubate in culture for 24 h. Peritoneal macrophages were also isolated from normal mice and treated with the drugs for 2 h. After treatments the macrophages were placed in fresh media and allowed to incubate 24 h. Supematants were isolated at various times during culture for immunocytochemical analysis.Both in vitro and in vivo studies showed enhanced immunostimulation after their respective treatments.