The purpose of the study was to examine the zinc and iron content of human lenses in different types of cataract and to investigate the possible influence of diabetes on the zinc and iron content of the lens. Iron and zinc of 57 human lenses (28 corticonuclear cataracts and 29 mature cataracts with a mean age of 70.6 +/- 16.1 and 74.7 +/- 11.1 yr, 41 nondiabetics and 16 diabetics) were determined by atomic absorption spectroscopy. The zinc content of human lenses was significantly increased in mature cataracts compared to corticonuclear cataracts (0.51 +/- 0.33 vs 0.32 +/- 0.20 micromol/g dry mass, p=0.012). The iron content of mature cataracts was also higher than in corticonuclear cataracts (0.11 +/- 0.09 vs 0.07 +/- 0.05 micromol/g dry mass, p=0.071). Furthermore, a significant increase of the lens zinc content could be observed with increasing lens coloration (light brown 0.33 +/- 0.17 vs dark brown 0.52 +/- 0.35 micromol/g dry mass, p=0.032). Diabetic patients seem to have both increased zinc and iron contents in the lens compared to nondiabetic subjects (zinc: 0.45 +/- 0.42 vs 0.40 +/- 0.22 micromol/g dry mass; iron: 0.12 +/- 0.10 vs 0.08 +/- 0.05 micromol/g dry mass). These data suggest a possible influence of the lens zinc and iron content on the development of lens opacification. Especially advanced forms of cataract and dark brown colored lenses show significantly increased zinc and iron content.