The effects of partner support on women with breast cancer were investigated utilizing a daily diary methodology. Fifty-four women who had recently been diagnosed with early-stage breast cancer completed daily diary measures of partner support amount and satisfaction, mood, cancer symptoms, and role functioning each day for 30 days. Results indicate that the relationship between support amount and satisfaction and the various outcomes differs depending on the level of support, suggesting different underlying mechanisms for average, same-day, and previous-day support. Women's average amount and satisfaction with support may help protect the women from the negative impact of breast cancer, while a woman's daily fluctuations in support seem to be related to her experience on that specific day. For previous-day support, amount appears to operate in the expected direction, while the effect of satisfaction is unclear. Thus, amount and satisfaction are both important when investigating effects of partner support.