Liposomes labelled with125I-labelled albumin were used as carriers for the introduction of albumin into vegetative and aggregation competent cells ofDictyostelium discoideum. The subcellular distribution of albumin and its degradation products was followed. The results show that 44 and 67% of the radioactivity incorporated by vegetative and aggregation competent cells, respectively, was found in soluble form in the cell. These figures fall to 26 and 34% in the presence of metabolic inhibitors with a concomitant increase of membrane-bound radioactivity. Differences in the mode of liposome–cell interaction in the two stages of development of the organism and the possibility that metabolic inhibitors may operate at the site of the vacuole–liposome fusion step are discussed.