The distribution of total plasma homocysteine concentrations in relation to the sex and age is described, in a population of Shiraz, South West of Iran and compared to those reported in other populations. Two hundred and one healthy males and 201 healthy females aged >15 y were randomly selected. Total Plasma homocysteine concentrations were measured using high performance liquid chromatography. The mean plasma homocysteine level was significantly higher in men (geometric mean 7.3µmol/L) than in women (geometric mean 6.3µmol/L, p<0.001). The geometric meanlevels for age ranges 15-25, 26-36, 37-47, 48-58, 59-69 and 70-80 years,were 5.9, 5.4, 5.2, 6.7, 7.3 and 7.6 µmol/L in women and 7.5, 8.7, 5.9, 5.9, 7.2 and 9.1 µmol/L in men respectively. The first data on homocysteine distribution ina representative sample from South West of Iran indicate that the ethnic differences have an important impact on homocysteine metabolism.