A colony of Amblyomma parvum was started with engorged females collected from cattle in the Province of Salta (25 degrees 01' S, 63 degrees 56' W), Argentina. The progeny of those ticks were fed on rabbits and the non-parasitic stages maintained at 27 +/- 1 degrees C, 83-86% RH in darkness. The life cycle (prefeeding period not evaluated) had a mean duration of 99.6 days. The mean time (days) for the different phases of the cycle were as follows: feeding period of females, 8.0; pre-oviposition period, 5.7; oviposition period, 17.5; minimum incubation period of the eggs, 31.8; feeding period of larvae, 3.2; premoult period to nymphs, 10.9; feeding period of nymphs, 4.7; premoult period to adults, 17.8. The oviposition pattern was typical of an ixodid tick, including a linear relationship between weights of engorged females and the number of eggs laid (r = 0.8659). The males increased 18% in weight after feeding on hosts (P less than 0.01). The mean recovery rates of larvae, nymphs and females were 28.2%, 95.3% and 90.7%, respectively. The nymphs moulting to females were heavier (6.8 +/- 0.69 mg) than those moulting to males (3.2 +/- 0.29 mg) (P less than 0.01). A comparison of biological values of A. parvum with American and non-American Amblyomma species is presented.