The paper deals with the issues of determining the reference value of specific activity of cesium-137 of Chernobyl origin when applying the radiocesium method to assess the loss of gray forest soil in the areas of spread of the microrelief of paleocryogenic origin in the periglacial region of the upper Oka basin. Paleocryogenic microrelief is recognized in spring satellite imagery available on Google EarthTM. The necessity of choosing a reference plot for a specific field that differs in microrelief, exposure, and the nature of soil cultivation is substantiated. The authors analyze the data, which they obtained during the field research in 2016−2019, on three agricultural fields located on the arable slopes of the northern and southern exposure in the upper Oka basin within the Orel district of the Orel Region. Three experimental plots, selected in close proximity to one another, differed both in exposure and in the content of humus, labile phosphorus and radiocaesium in the arable layer. Layer-by-layer soil sampling at block elevations within the reference plots located on watershed surfaces, gamma-spectrometric and agrochemical analyzes of soil samples allowed us to draw a number of systematically important conclusions. The first is that the reference value of radiocaesium in the arable layer should be determined within block elevations on the watershed surface of the slope or on inter-valley micro-water divisions on the water-divide surface (if it is not possible to select a reference plot on the watershed surface). The second is that the dimensions of the reference plots are determined by the size of the block elevations (the sizes of blocks in the area under study are 10−20 m). The third is that the reference value of radiocaesium should be determined individually for each field that differs in exposure and in the nature of the soil treatment. In the experimental plot, the reference value of the specific activity of cesium-137 increases in the following order: a field located on the water-divide surface of the northern exposure slope, with a grain rotation, with regular fertilizing (130.5 Bq / kg) - a field located on the watershed surface of the eroded slope southern exposure (174.7 Bq / kg) - a field located on the water-divide surface of a less fertilized and less eroded slope of the northern exposure (180 Bq / kg). The results of the study show that the use of the radiocaesium method in periglacial areas requires testing a fundamentally new approach to its implementation: at the stage of determining the reference value of radiocaesium, it is necessary to take into account the polygonal-block structure of the watershed surfaces.