Summary Forty-four female students with a tendency for constipation (mean age, 20.263.3 y) were asked to consume 30 g test pickles daily for 2 wk and were divided into 3 groups: viable-cell intake subjects (n514, 3.0310 5 colony-forming units of viable LAB (lactic acid bacteria) cells per sample), dead-cells intake subjects (n515, viable cells were heat sterilized), and placebo-intake subjects (n515, LAB removed from the pickles). g-Aminobutyric acid content of 75.163.2 mg per sample was noted, with no marked difference between samples containing viable and dead cells. Natural killer (NK)-cell activity (% specific lysis) in serum from dead-cell intake subjects was 37.5617.0% before the start of the test-food intake and 47.7620.1% after intake, indicating statistically significant effects (p,0.01). However, viable-cell intake and placebo intake subjects showed no statistically significant difference. The number of days with bowel movements significantly increased from 3.861.5 to 4.961.8 d in the dead-cell intake group, whereas a slight change from 4.661.5 to 5.161.7 d was observed in the viable-cell intake group. Additionally, the feeling of incomplete evacuation fell and a refreshed feeling increased among the subjects with constipation. Thus, marked enhancement of NK-cell activity and improved bowel symptoms were observed in subjects consuming pickles containing dead LAB cells.