Suppression of tumour necrosis factor alpha (TNF-alpha) and other interleukins by wormwood (Artemisia absinthium) extracts were reported recently in in vitro studies. The aim of the present study was to find out if this effect can be also be observed in Crohn's Disease (CD) patients where TNF-alpha appears to play an important role. In a controlled trial, 10 randomly selected patients suffering from CD were given in addition to their basic CD therapy 3x750mg dried powdered wormwood for 6 weeks. Ten patients, also randomly selected who met the inclusion criteria served as control group. Minimum score of 200 on Crohn's Disease Activity Index (CDAI) was required at baseline for inclusion in each group. Patients who received infliximab or similar were excluded from the trial. TNF-alpha level in serum were measured at baseline, and after three and six weeks. During this period all concomitant CD medications was maintained at the baseline dose levels. Average serum TNF-alpha level fell from 24.5+/-3.5pg/ml at baseline to 8.0+/-2.5pg/ml after six weeks. The corresponding levels in the control group were 25.7+/-4.6 (week 0), and 21.1+/-3.2 (week 6). On the clinical side, CDAI scores fell from 275+/-15 to below 175+/-12 in wormwood group with remission of symptoms in eight patients (CDAI score below 170 or reduction by 70 points), compared to only two in the placebo group (CDAI of placebo group 282+/-11 at baseline and 230+/-14 on week 6). IBDQ also reflected accelerated clinical response with wormwood. Of clinical significance were the findings that wormwood also improved mood of the CD patients, as reflected in Hamilton's Depression Scale. These findings provide a base to test wormwood in clinical conditions thought to be mediated by increased production of pro-inflammatory cytokines such as TNF-alpha.