Abstract: Heavy metal environmental pollution, especially with lead has become very disturbing, because it causes multiple negative effects in living organisms. It is known that lead is a potent inhibitor of ALA-D activity. The current investigations provide an attempt to find minimal critical level of lead that produces inhibitory effect of ALA-D activity of erythrocyte. In present study it has been also examined the effect of high temperature in activity of ALA-D. Research was performed in human blood hemolysate. For that purpose we selected a healthy human individual who has not been exposed to lead intoxication, does not smoke and does not consume alcohol. The negative correlation was estimated between Pb concentration and ALA-D activity in all concentration (2-100 μg%). Exception from this inhibition trend is the activity of enzyme at 60°C in lead concentration from 7-10 μg%. In concentration of lead above 7 μg% and in temperature of 37°C the activity of enzyme was low while in the same concentration bat in temperature of 60 °C the activity of enzyme was recovered. In high concentrations of Pb, the activity of ALA-D was significantly inhibited at 37°C in comparison to other temperatures (42°C, 50°C and 60°C).