"Pulse-chase" experiments with erythrocytes and reticulocytes prelabelled with 32P-Pi revealed a high turnover of the monoester phosphate groups of PIP2 in reticulocytes, which declines strongly during maturation [Maretzki et al., Biomed. Biochim. Acta 45, 1227-1236 (1986)]. The 3H-inositol uptake exhibits a strong maturational loss. A carrier-mediated uptake of inositol in reticulocytes is suggested. In reticulocytes PI, PIP and PIP2 incorporated 3H-inositol in the relative distribution of 86; 5 and 9%, respectively, but only PI to a minor extent in erythrocytes. A small release of 3H-labelled inositol phosphates was found in reticulocytes, which was not stimulated by extracellular calcium during incubation. Determination of the 32P/3H-ratio in double-labelled phosphatidylinositides in reticulocytes demonstrated a very slow turnover of the diester phosphate bonds compared with that of the inositol phosphate ester groups.