1. The effects of nadolol (or placebo) and carbimazole on thyrotoxic tremor were investigated in 18 thyrotoxic patients. 2. Both nadolol and carbimazole produced significant reductions in tremor power although nadolol did not cause any change in serum free tri-iodothyronine and free thyroxine concentrations. 3. The results are discussed in terms of the pathogenesis of thyrotoxic tremor and the potential usefulness of tremor in the investigation of adrenergic mechanisms in thyrotoxicosis.