The bird nasal schistosome Trichobilharzia regenti is a new agent of cercarial dermatitis. Cercariae are able to penetrate the skin of birds and mammals including man. The parasite then attacks the central nervous system. The present study has shown that schistosomula avoid penetration of blood capillaries and enter the peripheral nerves of the legs of mice and ducks as early as 1 day post-infection (p.i.) and 1.5 days p.i., respectively. These peripheral nerves are used as a route to the spinal cord. In the specific host (duck) schistosomula were found in the spinal cord from 2 days p.i. until 15 days p.i. and in the brain from 12 days p.i. until 18 days p.i. In non-specific hosts (mice; inbred strains BALB/c, hr/hr, SCID) living schistosomula were found in the spinal cord from 2 days p.i. until 21 or 24 days p.i. (depending on the mouse strain) and in the brain of two (BALB/c, SCID) of three inbred strains from 3 days p.i. until 24 days p.i. No correlation was found between the infection dose and clinical status of the experimental hosts. A high affinity of schistosomula for the peripheral nerves was also proved in vitro, suggesting a new type of migratory behaviour in schistosomatids.