In experiments conducted for three years, different organic substrates were used as additions to mineral soils, creating five horticultural substrates. Cadmium in the amount of 0, 2.5 and 10 Cd mg dm-3 and lead at rates of 0, 25, 100 Pb mg dm-3 were introduced into the studied substrates creating thereby a contaminated environment. In the prepared substrates, tomato, ‘Recento’ cultivar, was grown in 10 dm3 containers. The objective of the experiments was to investigate the dependence between the content of organic carbon and the content of Cd and Pb in horticultural substrates. It was found that the introduction of different organic substrates caused a decrease in the amount of soluble forms of cadmium and lead in the substrates.