Three sheep were infested 4 times with 100 Amblyomma americanum tick pairs and kept indoors until the natural termination of the infestations. Characteristics of the tick populations that show efficiency of feeding, fertility, and offspring development, and ELISA antibodies to tick salivary gland extracts were studied at each infestation. On average, female ticks fed on tick-naive sheep detached at 12.1 +/- 0.2 (mean +/- standard error) days, weighed 492 +/- 16.8 mg, engorged 40.7 mg per day, and 35% survived to detachment during the first infestation. During the fourth infestation, they detached at 17.3 +/- 0.8 days, weighed 321 +/- 14.4 mg, engorged 18.8 mg per day on average, and 23% survived to detachment. On average, oviposition of female ticks fed on tick-naive sheep started at 11.8 +/- 0.6 days of detachment, the egg mass weighed 236 +/- 13.2 mg, 43% of the female weight turned into eggs, and 89% of the ticks that detached survived to oviposition during the first infestation. During the fourth infestation, oviposition started at 15.1 +/- 0.5 days, the eggs weighed 103 +/- 9.9 mg, 13% of the tick weight became eggs, and 67% of the ticks survived to oviposition. On average, eclosion started at 35.4 +/- 0.9 days of oviposition and 83% of the egg batches hatched in the first infestation. During the fourth infestation, eclosion started on day 34.9 +/- 0.7, and 47% of the egg batches hatched. Anti-tick resistance was expressed as an inhibition of feeding, fertility, and offspring development.(ABSTRACT TRUNCATED AT 250 WORDS)