Three pyrimidine derivatives -methyluracil, hydroxymethacil (a new compound), and its lithium salt -were tested in model systems of differing complexity for antioxidant properties in comparison with the well-known antioxidant ionol. Tests for antiradical activity and for effects on spontaneous and Fe2+-ascorbate -or NADPH-dependent lipid peroxidation revealed high antioxidant activity (comparable to that of ionol) of the hydroxymethacil lithium salt.