A study of liveweight changes of alpaca adult males, females, and their progeny, was conducted through 3 seasons under COD tinuous grazing on natural grasslands on the Mediterranean range of the Chilean Central Zone. Liveweight changes were positive and highest in spring (100 to 200 g day'), moderate during winter (50 to 100 g day-l), and negative only at the end of summer and in fall (-110 to-150 g day'). Weight gains of new born alpacas were greatest (110 to 150 g day') in the first !I0 days after birth and Lhen decreased slightly, reaching values of 75 g day1 at 8.5 months old. Weight gains stabilized at 10 tu 20 g day' at 3years of age. The average annual fibre production was 1.57 and 2.36 kg in females and males, respectively; staple length varied between 8 and 10 cm.