In the Peruvian highlands, alpaca rearing areas are located between 4100 and 4700 m above sea level, with the finest fiber production believed to be associated with higher altitudes. The purpose of this experiment was to study the effect of differences in altitude on alpaca production, body weight (BW), clean fiber weight (FW) and fiber diameter (FD). Two areas with similar carrying capacities were identified at 4200 and 4600 m and stocked with 40 2-year-old (tuis), white, huacaya breed male alpacas in total. The experiment was conducted during two phases (phase 1: dry season; phase 2: wet season), with 4 × 28-day periods in each phase, plus a pre-experimental adaptation period of 28 days at 4200 m. Fiber samples were taken from a 10 cm2 area on the left flank region every 28 days. For phase 1, 20 alpacas were transported to 4600 m, while the remaining 20 were kept at 4200 m. In phase 2, 10 alpacas from each group were switched to the alternate elevations, while the remaining animals were kept at their respective altitudes. In general, BW, FW and FD increased continuously during the course of the trial. The standard error for BW least squares means was 0.9343 kg, with a significant difference (p < 0.0001) between periods. The initial FW (1.3 ± 0.3 g × 10 cm2) and FD (22.9 ± 2.6 μm) did not differ significantly between treatments, with the standard error for FW and FD being 0.1842 g × 10 cm2 and 1.0663 μm, respectively with significant difference (p < 0.0001) between periods, but not between treatments. In general, altitude treatments did not exert a significant effect on any of the variables measured. In contrast, time (period) effects were clearly evident for all the traits measured. Changes in response over time largely appeared to reflect the normal maturation processes of tuis and the availability of higher quality pastures during the wet season. Conclusion, altitude within the normal elevation range for alpaca production does not appear to significantly affect fiber production. © 2005 Elsevier B.V. All rights reserved.