A number of studies have reported an association between 5-HTTLPR, a polymorphism of the serotonin transporter gene, and the development of depressive states in response to a variety of distal and proximal stressors. We report here studies of the effects of the 5-HTTLPR polymorphism on the probability that an individual will develop mental maladaptation in 224 close relatives of patients with severe chronic mental disorders - schizophrenia and schizoaffective and affective psychoses. The ss genotype of the serotonin transporter gene contributes to the formation predominantly of manifestations of distress, reflected by increases on the hypochondriasis scale of the MMPI scale of factors such as the extent of the autonomic component of anxiety reactions and increased attention to own health, as well as increases in sensitivity. At the same time, the ss genotype was less likely to influence the appearance of depression and anxiety, as determined on the depression scale. These tendencies were more marked in males than females. Furthermore, males with the ss genotype were characterized by some increase in tension, suspicion, detachment, and attention difficulty (on the paranoia and schizophrenia scales). These data can be regarded as supporting the role of the short allele of the serotonin transporter gene in enhancing and modulating psychopathological reactions to chronic stress situations in relatives of mental patients.