Purpose: To investigate the relationship between the alkaline phosphatase (ALP) network of the marrow stroma and the haematopoietic regeneration after mice whole-body irradiation. Materials and methods: Three groups of mice were irradiated with a non-lethal ionising radiation dose: the fi rst one received an intraperitoneal injection of Levamisole, ALP inhibitor, 24 h before irradiation; the second one received an intraperitoneal injection of Lisinopril, haematopoiesis inhibitor, 24 h before irradiation; the third was left untreated, but irradiated. The fourth group, untreated and not irradiated, was the control. The total surface occupied by ALP positive processes, revealed by means of ALP cytochemistry in the marrow area, was evaluated semi-quantitively. Nucleated bone marrow cells were also counted. Results: ALP network began to increase 24 h after irradiation to reach a maximum after 72 h, when the bone marrow was almost become completely empty of the haematopoietic cells. This increase advances the haematopoietic recovery. This process was substantially delayed when the mice were injected with Levamisole 24 h before irradiation. On the contrary, ALP network increased strongly since the fi rst day after irradiation when the mice were injected with Lisinopril 24 h before irradiation. Conclusions: These data have indicated that the haematopoietic recovery and repopulation of the bone marrow were advanced by the ALP network recovery.