The effect of low power laser light upon the haematopoietic system of rats and also upon the basic haematological parameters was studied. A HeliumNeon continuous emission laser (632.8 nm; max. power 5 mW) and a Galium arsenide semiconductor pulse laser (904 nm; power 80 mW; pulse duration 200 ns) were used as light sources. Intact skin on the hind legs of rats was exposed, over a section of the femur. Peripheral blood analysis carried out before and after the experiments. These indicated that AsGa laser light induced a decrease in bone marrow mastocytes and peripheral blood basophils with an increase in the number of eosinophils. An increase in mitotic activity in the bone marrow was observed in the exposed groups of animals. No significant changes in Hb, Ht, erythrocyte or reticulocyte levels in the peripheral blood were noted, nor was there an increase in megakaryocyte emperipolesis.