Epidemiological studies point to an association between prenatal exposure to influenza and later schizophrenia. Such studies are consistent with neuropathologic reports demonstrating cytoarchitectural abnormalities in the hippocampus and parahippocampal gyrus suggestive of second trimester developmental anomalies. The hypothesis that prenatal exposure to influenza in the second trimester may induce hippocampal pyramidal cell disarray in mice was investigated. Between days 9-16 of pregnancy, 35 Balb/c mice were intranasally inoculated with either a mouse-adapted or non mouse-adapted pool of Influenza A/Singapore/1/57 (H2N2), and 10 controls were inoculated with normal saline. Offspring were sacrificed on day 21 postpartum. Microscopic examination of the CA1-CA2 junctional areas in the offspring of mice exposed to influenza failed to demonstrate excess pyramidal cell disarray when compared with influenza-free, age matched controls. There was evidence that disarray was greater among those exposed on day 13 of pregnancy. Analyses of the data by sex and severity of maternal infection failed to reveal any significant effects.