Our findings in the Helsinki Influenza Study and the Danish Forty Year Study lead us toconclude that a 2nd-trimester maternal influenza infection may increase risk for adultschizophrenia or adult major affective disorder. More recently we have also reported an increaseof unipolar depression among offspring who were exposed prenatally to a severe earthquake (7.8on the Richter scale) in Tangshan, China. Among the earthquake-exposed males (but not thefemales), we observed a significantly greater depression response for those individuals exposedduring the 2nd trimester of gestation. These findings suggest that maternal influenza infectionand severe maternal stress may operate (in different ways) as teratogens, disrupting thedevelopment of the fetal brain and increasing risk for developing schizophrenia or depression inadulthood.