Levels of haemoglobin, haematocrit, number of red cells and leukocytes, haematological index (MCV, MCH, MCHC, DEI, MPV), sedimentation rate, iron, parameter related to accumulation and transport of iron (transferrin, ferritin, iron binding capability, transferring saturation index) and platelets were determined in blood samples of opiate addicts and they were compared with these results obtained in a control group. For both sexes, the levels of haemoglobin, haematocrit, iron and platelets were similar in the control groups and opiate addicts. Opiate addicts females presented a number of red cells and platelets higher and lower respectively than the correspond values of the control group. The haematological index in opiate addicts were higher than the values in the control groups for overall and considering males and females independently. The levels of ferritin in opiate addicts males were higher than these levels found in control groups, occurring the contrary in the females. Opiate addicts males and females included in the methadone maintenance treatment program (MMTP) presented similar values of haemoglobin, haematocrit, number of red cells and leukocytes than the corresponding opiate addicts non-included in MMTP, except opiate addicts males, who showed lower haematocrit values.