<p>Mosses and lichens are often used to assess atmospheric deposition of ²¹⁰Pb. The most widely used method for determining this isotope is gamma spectrometric analysis. There is often a need to enhance the sensitivity of the method, which can be achieved by pre-concentrating ²¹⁰Pb. The simplest method in this case is direct dry ashing according to commonly accepted standardized procedures. However, the question of potential losses of ²¹⁰Pb during the combustion of mosses and lichens remains unclear. The main objective of this study is to investigate the effect of the dry ashing procedure on the accuracy of determining ²¹⁰Pb concentrations in the studied samples. The conducted experiment showed that ashing samples with low (&lt; 8%) ash content, which includes all mosses and lichens, at a temperature of 450&#xa0;°C leads to significant losses of ²¹⁰Pb (up to 40%). For samples with an ash content &gt; 14% (litter), the losses of this isotope do not exceed 3–4%. For both groups, the value of ashing losses has a nearly linear dependence, inversely proportional to the ash content in the studied material. The obtained relationships allowed us to calculate the corrections necessary to account for ²¹⁰Pb losses during ashing of both low and high ash materials. The application of several statistical tests demonstrated good convergence and consistency of the results of ²¹⁰Pb determination obtained by direct measurement in unashed samples and those calculated through the measured activity of this isotope in ashes, corrected for ashing losses.</p>