Primary tissue culture cells of developing larvae of Amblyomma americanum were administered to guinea-pigs never previously exposed to ixodid ticks. Guinea-pigs were given 1 X 10(6) primary culture cells on Days 0, 7 and 21 by subcutaneous injection and challenged with male and female A. americanum on Day 35. A significant degree of induced host tick resistance was expressed by reduced engorgement weight of females, reduced oviposition by those females which did obtain a blood meal, and by death of ticks at the attachment site. Resistance induced by A. americanum primary culture cells stimulated a significant degree of resistance to infestation with Dermacentor andersoni adults.