Erucylphosphocholine (ErPC) is a new alkylphosphocholine derivative with distinctly reduced hemolytic activity, thus allowing intravenous (i.v.) injection. ErPC was investigated in methylnitrosourea-induced rat mammary carcinoma, the signal tumor for these classes of alkylphosphocholines, using peroral (p.o.) and i.v. dosages ranging from 15-120 μmol/kg/day. After 5 weeks of treatment, i.v. administration of ErPC was not only equipotent to p.o. administration at three to five times lower doses but also caused complete remissions in more than 50% of the animals. Such responses were not obtained with p.o. administration of ErPC or hexadecylphosphocholine (HPC, miltefosine); they demonstrate a distinctly improved therapeutic efficacy of i.v. ErPC in the model investigated. Moreover, since i.v. ErPC reduces the drug load to the gastrointestinal tract, which is the main target of alkylphosphocholine-related side effects, such effects are expected to be diminished with this mode of treatment. In addition, ErPC was compared with HPC, the clinically used standard alkylphosphocholine, in a panel of 10 tumor cell lines. On a molar basis, ErPC was less active than HPC in four of six tumor cell lines derived from solid tumors, but more active in three of four leukemic cell lines. The overall similar sensitivity profiles of ErPC and HPC indicate that the advantage of ErPC seen in vivo, at least in part, is due to improved pharmacokinetic properties.