Background and objectives Previous data that showed maintenance of reticulocyte percentage in whole blood stored in CPDA ‐1 have led to the assumption that reticulocyte maturation becomes arrested during refrigerated storage. However, reticulocyte behaviour in red‐blood‐cell units stored in additive solutions has not yet been studied. This study was thus aimed at determining reticulocyte count and reticulocyte subtypes in red‐blood‐cells units stored in AS ‐1. Materials and methods Reticulocyte percentage and subtypes were determined by flow cytometry with thiazole orange in six red‐blood‐cells units stored in AS ‐1. Results Reticulocyte count was 26·8 ± 4·6 × 10 9 /l at week 0·5 and 8·2 ±2·9 × 10 9 /l at week 6. Total haemolysis during storage was 0·19 ± 0·08%. High‐fluorescence reticulocytes were 2·0 ± 3·2 × 10 9 /l at week 0·5 and decreased by weeks 2, 4 and 6. Low‐fluorescence reticulocytes were 22·1 ± 3·1 × 10 9 /l at week 0·5 and decreased by weeks 4 and 6. Conclusion A significant decrease in reticulocytes occurred during red‐blood‐cells units’ storage in AS ‐1. Even if it were assumed that all of haemolysed cells during storage were reticulocytes, there are a number of them whose disappearance cannot be explained by this mechanism. Changes observed in reticulocyte subtypes suggest that they mature during storage.