Two experiments were performed to determine the anthelmintic effect of some phytogenic feed additives on a mild infection of Ascaris suum in growing and finishing pigs. Usually, an infection of A. suum is controlled by using conventional synthetic drugs. Organic farmers, however, prefer a non-pharmaceutical approach to worm control. Therefore, phytotherapy could be an appropriate alternative. In the first experiment, a commercial available organic starter diet was supplemented with 3% of a herb mixture, adding 1% Thymus vulgaris, 1% Melissa officinalis and 1% Echinacea purpurea to the diet, or with 4% of a herb mixture, thereby adding the mentioned herbs plus 1% Camellia sinensis (black tea). A negative control group (no treatment) and a positive control group (treatment with conventional synthetic drug flubendazole) were included. In the second experiment, the anthelmintic properties against A. suum of three individual herbs, Carica papaya, Peumus boldus and Artemisia vulgaris, each in a dose of 1%, were tested. Pigs were infected with 1000 infective worm eggs each. Each experiment was performed with 32 individually housed growing pigs (8 replicates/treatment), which were monitored for 67 days. It was hypothesized that the herbs would block the cycles of the larvae, thereby preventing the development of adult worms. Therefore, phytogenic feed additives were not supplied during the whole experimental period, but only from the start until D39. Pigs were inoculated with infective worm eggs during five consecutive days (D17-D21). At D67 all pigs were dissected, whereafter livers were checked for the presence of white spots. Also numbers of worms in the small intestine were counted. In experiment 1, the numbers of worm-infected pigs were similar for both the herb supplemented (groups 3 and 4) and the unsupplemented (group 1) treatments (5-6 pigs of 8), while the treatment with flubendazole (group 2) resulted in 0 infected pigs. In experiment 2, herb addition (groups 2-4) did not significantly reduce the number of worm-infected pigs compared to the negative control (group 1). It can be concluded that the tested herb mixtures and individual herbs in the diets of growing and finishing pigs did not decrease the number of pigs which were infected with A. suum, although the herb mixture without black tea and also boldo leaf slightly (P<0.10) reduced the number of worms in the intestinal tract. The tested herb mixtures and individual herbs did not affect the performance of the pigs.