A comparison of chemical constituents of fresh and conserved samples of Agaricus bisporus was made. The crude protein and crude fat contents were practically unchanged but a decrease in dry matter content and a remarkable decrease in ash content were found. The concentrations of some minerals (Cd, Mn, Zn) were unchanged, indicating that the solubility was not good or the soluble, free forms of element were not present in large amounts. Another group of elements (B, Cu, K, Mg, P, Se) showed a decrease to varying extents because the presence of the free forms of the elements was high. Unfortunately this tendency was with regard to elements that belong to the biologically more valuable mineral components (K, P, Mg). Higher Cr-, Ni-, and Hg-concentrations of conserved mushroom samples are not beneficial characteristics. The extremely high Na level of the conserves (and therefore the changed, unbeneficial K/Na rate) is a hazardous factor to some groups of consumers (patients of high blood pressure and in general people with cardiovascular problems). According to the presented data there are some negative consequences (most of all the changes in minerals) derived from the classical technology of conservation which diminish the nutritional value of the mushroom.