Passive cutaneous anaphylaxis tests were used to examine the IgE respo
nses of cats repeatedly infected with the filarial nematode Brugia pah
angi. Specific IgE was usually detected only in those cats that killed
their adult worms and rarely in those cats in which adult worms survi
ved for long periods. We suggest that this specific IgE is actively in
volved in killing adult worms in the lymphatics.