The comments by Dr Lotti and his colleagues are very interesting and in accord with observations made in the course of our study (Archives 136:50-56, 1976). Seven of nine individuals we described who were treated with propranolol hydrochloride alone had a reduction in circulating serum T3 concentrations. In two patients, this was associated with a spontaneous remission of thyrotoxicosis. However, in five others similarly treated, serum T3 concentrations fell to levels lower than pretreatment values. Only one individual treated with propranolol alone had a rise in serum T3 concentrations during the period of observation. These changes, although admittedly relatively small and not statistically significant, would seem to be in accord with the unpublished observations of Dr Lotti and his associates.