Degradation of chlorophyll was studied in leaves of spinach grown in soil containing cadmium and tetracycline, based on spectroscopic measurements and biochemical analyses of plant extracts. It was shown that plant exposure to the highest levels of tetracycline and cadmium resulted in 64% and 68%, respectively, reduction in chlorophyll content. The chlorophyll degradation rate constants were determined, and they were found to increase with increasing doses of tetracycline and cadmium. The rate constant of chlorophyll degradation by tetracycline ranged from k = 960 M⁻¹ day⁻¹ to k = 2180 M⁻¹ day⁻¹, and the rate constant of chlorophyll degradation by cadmium ranged from k = 1130 M⁻¹ day⁻¹ to k = 2580 M⁻¹ day⁻¹, depending on dose. Plant stress responses to tetracycline are much stronger than to cadmium, as is visible from the activity of guaiacol peroxidase and catalase. However, phytotoxicity of cadmium, measured by the rate of chlorophyll degradation and enzyme activities, is much higher compared to tetracycline. The spectroscopic measurements were taken 10 days after tetracycline and cadmium were added to the reagent grade chlorophyll which was used at the concentration of chlorophyll in plants. Changes in absorption and fluorescence spectra are likely to result from removal of magnesium from the chlorophyll molecule, and thus they indicate the formation of pheophytin. Cadmium, on the other hand, is probably bound into the chlorophyll molecule, substituting its magnesium.