Our previous work indicated that gay males ultimately found to be seronegative showed impaired lymphocyte proliferative responses to phytohemagglutinin (PHA) and pokeweed mitogen (PWM) upon entering a study in which they would be notified of their human immunodeficiency virus-Type 1 (HIV-1) antibody status. To examine the degree to which alterations in various neuroendocrine and psychological markers might be related to this phenomenon we measured plasma cortisol, beta-endorphin, denial coping strategies, intrusive thoughts related to AIDS risk, and several affective distress markers in 46 HIV-1 seronegative subjects at each of the timepoints previously studied. Results indicated that cortisol levels were elevated at study entry and decreased across the subsequent five-week period--mirroring the changes in mitogen responsivity across these timepoints. Analyses of individual differences showed that higher baseline cortisol and lower denial coping scores predicted lower PHA values at baseline. Persisting intrusive thoughts about risk of HIV-1 infectivity (after seronegativity notification) were consistently associated with higher plasma cortisol levels. Finally, beta-endorphin levels did not change significantly across the 10-week observation period, were not associated with psychological variables, and were inconsistently associated with immune functioning.