Colony-stimulating factor (CSF) activity induction by lipophilic derivatives of three muramyl peptides, glyceryl dipalmitate-MDP derivatives, was studied in vivo and in vitro and compared to the activity of the same compounds incorporated within freeze-dried liposomes. Two lipophilic derivatives (MDP-GDP and MDPGBe-GDP) were able to induce CSF activity in vivo and in vitro. The incorporation of these compounds within appropriately designed liposomes composed of distearoylphosphatidylcholine and phosphatidylserine (DSPC/PS) increased their ability to induce CSF activity in vivo but completely abrogated their ability to induce CSF activity in vitro. Furthermore, the phospholipid composition of liposomes influenced the efficacy of glycopeptide liposomal incorporation. Thus, the serum CSF-inducing effect of MDP-GDP was considerably enhanced by incorporation of this compound within liposomes composed of DSPC/PS at a molar ratio 7:0.3 but was not modified if the DSPC/PS molar ratio was 7:3. The lipophilic derivative of MDP (D-D), MDP (D-D)-GDP, was unable to induce CSF activity in vivo or in vitro but surprisingly became active in vivo after entrapment within DSPC/PS liposomes (molar ratio 7:0.3). Our results show that appropriate liposomes may be suitable carriers to deliver CSF activity-inducing agents to macrophages in vivo.