It was the aim of the research to investigate insomnia in healthy volunteers. One hundred healthy volunteers from sixteen to seventy five years old (50 females and 50 males) were investigated. Biochemical aspects of insomnia were determined. Because depression and insomnia are closely linked, correlation between insomnia and depression was studied. The degree of depression was evaluated and means of its prevention was determined. The index of serotonin in blood plasma platelets was determined because the serotoninergic system is involved in the regulation of sleep and wakefulness. Low Serotonin levels are believed to be linked with depression, insomnia; when levels of serotonin are brought up to normal, sleep falls into place. Sleep disturbances was revealed in 85% persons, of which 32%, had difficulties to fall asleep; moderate insomnia was found in 16% persons; severe depression was found in 30% persons. Serotonin index in blood plasma platelets was low in 25% persons, moderate--in 10% persons and high in 65% persons. It is concluded that depression is a main factor of insomnia; treatment includes drug therapy and psychoreabilitation.