The study was conducted in a period from May to November on young slaughter turkey-toms of the heavy (Big 6) and medium-heavy type (BUT 9), raised from 7 to 22 weeks of age indoor – in a brooder house (control group) or under a shelter with access to open-air runs (experimental group). The stocking density was 35 kg b.w. per m2 of area in the house or under the shelter. The surface area of the runs was twofold larger than that of the shelter. Blood for biochemical analysis was collected from turkey-toms aged 6, 10, 14, 18 and 22 weeks. The values of plasma biochemical parameters indicated the occurrence of periodical differences between the types of turkeys and management systems. At 22 weeks of age, turkeys raised under a shelter had higher plasma levels of glucose (by 64 mg dl⁻¹), total cholesterol (by 11 mg dl⁻¹) and uric acid (by 0.83 mg dl⁻¹), in comparison to birds raised indoor. At 14 and 18 weeks the plasma levels of total lipids were also higher in the experimental group, by 107 and 125 mg dl⁻¹ respectively. The plasma activity of lysozyme and alanine aminotransferase was affected by the housing system and showed higher individual variation. Differences dependent on the type of turkeys were observed in some weeks only, and concerned the plasma levels of total protein and alkaline phosphatase activity at 10 weeks, HDL cholesterol and lysozyme activity at 6 weeks, total cholesterol at 6 and 18 weeks, alanine aminotransferase activity at 6 and 10 weeks. The results of the present study can extend our knowledge with regard to some plasma biochemical parameters of two types of slaughter turkeys with no health problems, fed identical diets and raised under varied environmental conditions during five periods of their life. No significant changes were recorded in blood plasma biochemistry of turkey-toms kept under a shelter, as compared to those raised traditionally in a brooder house.