Little accumulation of fluid-phase markers, lucifer yellow CH (LY) and [14C] sucrose, was observed in 13762NF rat mammary adenocarcinoma clone MTF7, when a cell monolayer was incubated at 37°C for 60 min with reverse-phase evaporation vesicles (REVs) containing the markers. However, time-dependent accumulation was observed when the REVs were preincubated with polymorphonuclear neutrophils (PMNs) and added to the tumor cell layer. In contrast, accumulation of liposomal lipid marker, [3H]dipalmitoylphosphatidylcholine (DPPC), was independent of PMNs and approximately 10 times faster than those of the fluid-phase markers. The PMN-mediated transfer of LY and sucrose from REVs to MTF7 cells is attributed to PMN binding to the tumor cells and possibly high concentrations of the marker molecules in the unstirred layer of the tumor cells. The latter could have resulted from continuous phagocytosis and exocytosis of REV contents by PMNs. DPPC transfer must be spontaneous and could be simply collision-mediated. Significance of these in vitro observations is related to the role of PMNs in metastasis in vivo and the potential for drug delivery targeted to metastatic cells. © 1989.