Аннотация:This chapter presents the history of the first period of UPE study (1923–1948), completely devoted to UPE of ultraviolet range. It was called mitogenetic radiation due to ability to stimulate mitoses in some biological objects and was mainly observed by means of biological detectors (onion roots, yeast, bacteria, etc.). Here, we trace the timeline of its study from the very beginning (A.G. Gurwitsch’s investigation of spatial and temporal dynamics of mitoses), the discovery of mitogenetic radiation, to the period of its multidirectional large-scale research and finally to dramatic ceasing of works. Milestones of mitogenetic research are briefly presented, their specifics mainly implied by biological detection of radiation are analyzed, and the reasons for the mitogenetic research rise and fall are discussed. The authors consider this early period of UPE underestimated taking into account both its relation to the subsequent study of UPE of visible and infrared ranges and significance of scientific results, which were proved some decades later (free-radical mechanism of UPE generation, existence of peptide tumor markers in blood and others).