Twelve patients with Charcot-Marie-Tooth disease type 1 (CMT1) and 11 with type 2 (CMT2), with a clinically similar range of muscle weakness of foot dorsiflexion, were subjected to macroelectromyographic (macro-EMG) examination and muscle biopsy of the tibialis anterior (TA) muscle in order to elucidate the denervation-reinnervation process in the two CMT forms. The macro-EMG examination showed higher median amplitude values and median area values for the CMT1 patients, with a mean value of 1,515 +/- 1,222 microV and 3,953 +/- 2,613 microV. ms, respectively, than for the CMT2 patients, with a mean value of 865 +/- 971 microV and 2,525 +/- 2,575 microV. ms, respectively. When corrected for muscle fiber area, the difference was statistically significant for amplitude (P < 0.01) and area (P < 0.05). For CMT1 patients, the increase of macro-EMG potentials varied from 2 to 14 times and for CMT2 patients from less than 1 to 8 times larger than corresponding age-matched values. Muscle biopsies of TA showed that the type I fiber percentage was significantly higher (P < 0.05) in the CMT1 patients (99 +/- 2.2%) than in the CMT2 patients (86 +/- 12.3%). Morphometric data showed a significantly higher (P < 0.05) mean type I fiber area in the CMT2 patients (8,130 +/- 4,721 microm(2)) when compared with the CMT1 patients (5,066 +/- 3,431 microm(2)). The present data indicate that denervation in CMT1 is associated with prominent collateral reinnervation but only minor muscle fiber changes, whereas in CMT2 there is only minor collateral reinnervation but prominent muscle fiber changes including significant muscle fiber hypertrophy.