The study of long latency muscle reflexes evoked by electrical stimulation of the digital nerves of the index finger and recorded from the first dorsal interosseous muscle with a mean latency of 50 ms provided some evidence on the potential existence of a transcortical loop. The method of long latency relexes can be used to advantage in electrophysiological diagnosis of disorders of the central nervous system, in stimulatory therapeutic rehabilitation and in motor reeducation. The study of supraspinal modulation of the H-reflex excitability curve by dermal and light stimuli inducing long loop reflexes yielded physiological characteristics of its course in healthy subjects and in patients with disorders of the central nervous system. The most striking abnormality of the curves was recorded in the different degree of their facilitation and in the absence of late inhibition in individual nosological units. The method served as the basis of the diagnostic test for the detection of cerebral dysfunction in arterial hypertension, focal cerebral lesions, and neurasthenias.