The effect of the addition of two commercial bacterial starters on mineral oil degradation in two soils was studied : CS-O soil (10% mineral oil) and CS-OH soil (10% mineral oil + 45 mg/Kg HCH). Respiratory activity as well as degradation was determined. The two starters enhanced biodegradation in both soils without any significant difference due to HCH ( Hexachlorocyclohexane) presence in CS-OH soil.