This study reports on clinical and electromyographical findings which were obtained from an examination of male dizygotic twins and their father, who all suffered on a paramyotonia congenita. A simple coldness test can be used to distinguish paramyotonia congenita from myotonia congenita. Systematic cooling of the muscle of subjects with paramyotonia congenita leads to muscle stiffness and paresis, and finally to paralysis. An electromyographic analysis was carried out at various degrees of coldness. More than 300 paramyotonic series of discharges were analysed in respect to duration, amplitude and frequency. The results showed that the paramyotonic series are more similar to those of dystrophia myotonica than those of myotonia congenita.