Seventy-four crossbred beef steers (average BW = 239.2 + 10.7 kg) were used in a randomized complete block to evaluate the use of an extended-release eprinomectin (ER) on performance and fecal worm count during grazing. Steers were stratified and blocked by BW into sixteen 1.2-ha pastures of annual ryegrass, and pasture was randomly assigned to one of 2 treatments: a single injection of an extended release eprinomectin (ER) or 2 injections (d 0 and d 64) of a typical anthelmintic used in stocker operations (doramectin; DOR). Steers were individually weighed and fecal samples collected on d 0 and 114. Steers in the DOR group were re-worked on d 64 for a second dose of DOR. Data were analyzed as a mixed model with block considered random and treatment considered fixed, LSMEANS were separated using PDIFF. Pasture was the experimental unit. No differences (P = 0.36) were noted in initial BW (238.9 vs. 239.6 kg for DOR and ER, respectively), however at final BW, steers treated with ER (366.4 kg) were heavier (P = 0.04) than steers treated with DOR (357.8 kg). Moreover, steers treated with ER had greater ADG than DOR (P = 0.05; 1.11 vs. 1.04 kg/d for ER and DOR, respectively). As a result, steers treated with ER had greater gain per ha compared with steers administered DOR (P = 0.05). Due to the greater cost of ER and despite reworking costs of DOR, overall working cattle cost was greater for ER compared with DOR (P = 0.009; $41.44/hd vs. $39.83/hd for ER and DOR respectively. Total pasture cost per ha was greater (P = 0.009) for ER ($99.82/ha) compared with DOR ($99.37/ha), however increased weight gain resulted in decreased cost of gain (P = 0.04) for ER ($1.13/kg) compared with DOR ($1.19/kg). No differences among treatments (P = 0.66) were noted for fecal egg count at d 0, nor were any differences detected for fecal egg count at d 114 (P = 0.32), with a tendency (P = 0.13) for decreased percentage of fecal egg count associated with ER (88.9%) when compared with DOR (76.1%). Despite the greater costs associated with ER and similar fecal egg control compared with DOR, ER resulted in greater performance and decreased cost of gain.