1. An experiment was undertaken with 44 finishing steers (initially of more than 400 kg live weight) into the effects of copper and cobalt treatments. 2. Significant responses to copper treatment of up to 0·41 kg per head per day of live-weight gain were obtained. 3. A different response to copper treatment between Friesian and beef-type (Hereford or Devon) steers reflected not a true breed effect but a difference in initial copper status. 4. Cobalt bullet therapy proved to be ineffective in maintaining normal plasma vitamin B12 concentrations over the course of the experiment although liver cobalt levels were generally adequate.