This study was carried out in 50 subjects meeting exclution criteria. Minimental state examination (MMSE), Hamilton depression rating scale (HDRS), brief psychiatric rating scale (BPRS) were applied and serum levels of magnesium (Mg) were determined in the subjects includad the study. Subjects were divided into classes according to the scores of MMSE, HDRS, BPRS and serum Mg levels were compared to each group. Moreover, serum levels of Mg were compared to all groups classed according to age and sex. In addition, the relations between all variable scores were investigated. When the groups were compared as HDRS and BPRS scores, Mg serum levels were found significantly increased in the groups with low HDRS and BPRS scores. When subjects were classified according to MMSE scores, Mg levels were found significantly increased in the group with low MMSE scores (in high cognitive disrupted group). When subjects were classified according to sex and age, Mg levels were found significantly increased in th egroup of male and over than 45 years old. Severity of depression and serum levels of Mg tend to be a positive correlation between each others. In conclusion, low serum levels of Mg may be a secondary biologic criteria associated with depression and psychotic symptoms.