Based on the original data from two double-blind, randomized, placebo-controlled clinical trials and the acute phase of a long-term study that investigated the antidepressant efficacy of St. John's wort extract WS 5570, we present a re-analysis of a subset of patients suffering from an acute episode of mild depression according to DSM criteria. Out of a total of more than 1,200 patients included into these trials 217 had a pre-treatment total score < or =20 points on the 17-item Hamilton Rating Scale for Depression (HAMD) and were eligible for our re-analysis. They received 600, 900, or 1,200 mg/day WS 5570 or placebo for 6 weeks. In patients treated with WS 5570 the HAMD total score decreased by averages of 10.8 (600 mg/day), 9.6 (900 mg/day), and 10.7 (1,200 mg/day) points between the pre-treatment baseline value and the end of acute treatment, compared to 6.8 points in the placebo group (p < 0.01 for all pairwise comparisons of WS 5570 against placebo). This corresponded to average relative decreases by 49-57% for WS 5570 and by 36% for placebo. The rates of responders (i.e., patients with a HAMD total score decrease > or =50%) were 73%, 64%, 71%, and 37% for WS 5570 600 mg/day, 900 mg/day and 1,200 mg/day, and placebo, respectively. At the end of acute treatment 57% of the patients treated with WS 5570 600 mg/day, 33% in the 900 mg/day group and 62% in the 1,200 mg/day group, as well as 25% in the placebo group were in remission (HAMD total score < or =7 points). The analysis shows that St. John's wort extract WS 5570 has a meaningful beneficial effect during acute treatment of patients suffering from mild depression and leads to a substantial increase in the probability of remission.