To clarify the characteristics of parkinsonian and ataxic gaits, we analyzed electromyograms (EMGs) of the thigh and leg muscles, angular displacements of the hip and leg joints, and floor reaction forces during free walking for each gait phase in 16 patients with Parkinson's disease (PD) and 14 ataxic patients with cerebellar degenerations. We studied 17 healthy elderly subjects whose walking speed was similar to that of patients with moderate disease. Free walking by PD patients was characterized by low maximum activity of the gastrocnemius/soleus (GC) and tibialis anterior (TA) muscles. Ataxic patients showed high activity of GC and TA during the period when these muscles were not active in normal walking. The ratio of changes of EMG of the distal muscles to changes in angular displacement of the ankle (DeltaEMG/Deltaangle) was reduced in GC of PD patients in ankle dorsiflexion, whereas it was high in GC and TA of ataxic patients in ankle dorsiflexion and plantarflexion, respectively. Changes in DeltaEMG/Deltaangle coincided with those in proprioceptive reflexes reported previously. Our results showed that measurement of EMG for each phase revealed disease-specific factors, and that of DeltaEMG/Deltaangle might be a conventional clue for estimation of reflexes for these gait disorders.