- Homocysteine is reported to be a risk factor for schizophrenia. The methionine loading test evaluates the summation of a multitude of enzymatic pathways associated with homocysteine metabolism. Using a challenge paradigm, we measured homocysteine levels in 10 chronic schizophrenia patients and five controls at baseline and 3h after 100mg/kg oral methionine. This pilot study failed to detect a gross abnormality of plasma homocysteine level after acute methionine load in patients with schizophrenia. Elevations in plasma homocysteine reported in schizophrenia do not derive from a dynamic abnormality in methionine metabolism in this challenge paradigm.