The authors report two male cases of liver ornithine carbamyl transferase deficiency. In one the disease occurred at 8 years of age with hyperammoniemic coma leading to death in 48 hours. In the second case, symptoms appeared on the sixth day of life but the outcome was favorable. The child is normal at 15 months. In both cases, there was a residual 6-10% OCT activity. These observations are similar to two other male cases in the literature and are different from the male neonatal fatal form in which the deficiency is virtually total. They underline the genetically heterogeneous nature of OCT deficiencies and the fact that in this X-transmitted trait, hemizygotes can preserve a functional enzymatic activity compatible with life.