The primary purpose of this exploratory study was to compare percentages of natural killer (NK) cells and activated NK and T cells, and both cytotoxic and in vitro cytokine production activity in women with and without symptomatic irritable bowel syndrome (IBS). A secondary purpose was to examine the relationships of psychological distress and low sense of coherence with immune function indicators and stress hormones. NK cell percentage and activity have been shown to vary in response to many psychological and physiological stressors. The authors compared 2 groups of women: symptomatic IBS (n = 12) and control (n = 12). Between-subject variability for all immune measures was large. The percentage of activated NK and Tcells was significantly lower in the IBS group compared to control (Mann-Whitney U = 30, P = 0.05). Relationships were significant between activated NK and T cell percentage and depression, anxiety, and overall distress (r = -0.54, -0.49, and -0.47, respectively, P < 0.03) and between interferon-gamma production and anxiety (r = -0.45, P < 0.03). There was a trend toward a positive relationship between sense of coherence and NK cytotoxicity (r = 0.39, P = 0.11). Thesefindings are important because they suggest that nursing interventions targeting ongoing physical and psychological distress might also be helpful in improving immune function.