Psychological stress has been associated with reduced immune response to a variety of vaccinations. This study is the first to examine antibody status after vaccination with a conjugate vaccine, in which a polysaccharide antigen is conjugated to a protein to elicit a thymus-dependent antibody response. Sixty undergraduate students, who had received the meningitis C conjugate vaccine before recruitment, attended a single testing session. They provided a blood sample and completed a battery of questionnaires, including the Life Events Scale for Students, Perceived Stress Scale, and General Health Questionnaire (GHQ-28). Both meningitis C-specific antibody titer and the serum bactericidal assay titer to whole meningitis C bacteria were assayed. High perceived stress, but not life events stress, was associated with low antibody titers. Poor antibody titers were also predicted by relatively low levels of psychological well-being as measured by the GHQ-28. Of the GHQ-28 subscales, anxiety/insomnia and social dysfunction were associated with antibody status. No psychological variables emerged from bivariate analyses as predictive of the adequacy of bactericidal titer. This study provides the first evidence that antibody status after a conjugate vaccination may be susceptible to psychological influences.