Abstract <p><i>Ortho</i>-phthalic acid esters (phthalates) are widely used in the chemical industry. At the same time, these are natural compounds produced in large quantities by plants and other organisms. A comparative analysis of industrial and natural substances is carried out, and differences in their composition are indicated. Phthalates have a broad spectrum of biological activity. The reasons for the discrepancies in the assessment of the effects of these compounds on animals and humans are considered. The need to differentiate natural and synthetic compounds in environmental studies is emphasized. An analysis of possible functions of <i>ortho</i>-phthalates in plants is given.</p>