An electrode array was implanted for chronic recording of EMG activity in both soleus muscles (SOL) in adult albino rats (Wistar strain) of 250 g mean body weight. After 12-13 days, surgical thyroidectomy was performed and the postural EMG activity in both SOL muscles up to 16 weeks after the operation was quantitatively compared (spikes per minute) with the EMG activity before the operation. The results showed that the EMG activity in the SOL is significantly decreased after thyroidectomy.