This study examined daily stress processes among 75 married couples across 20 assessments during a 6-month period. The somatic and psychological effects of common everyday hassles were investigated. Overall, there was a significant relationship between daily stress and the occurrence of both concurrent and subsequent health problems such as flu, sore throat, headaches, and backaches. The relationship of daily stress to mood disturbance was more complex. The negative effects of stress on mood were limited to a single day, with the following day characterized by mood scores that were better than usual. Furthermore, striking individual differences were found in the extent to which daily stress was associated with health and mood across time. Participants with unsupportive social relationships and low self-esteem were more likely to experience an increase in psychological and somatic problems both on and following stressful days than were participants high in self-esteem and social support. These data suggest that persons with low psychosocial resources are vulnerable to illness and mood disturbance when their stress levels increase, even if they generally have little stress in their lives.