We have evaluated the possible apoptotic effect of benzoxazine (BO) derivatives. For that purpose, we tested the induction of apoptosis by 6-[1-hydroxy-2-(1H-1-imidazolyl)ethyl]-4-methyl-3,4-dihydro-2H-1,4-benzoxazin-3-one (FO4) and 6-[1-[(4-chlorobenzyl)oxy]-2-(1H-1-imidazolyl)ethyl]-4-methyl-3,4-dihydro-2H-1,4-benzoxazin-3-one (FO5) BO analogues in mouse thymocytes in vitro, a sensitive experimental model that has been widely used to study various apoptotic agents. Results indicate that FO4 and FO5 are able to induce thymocyte apoptosis and that this effect is dose-related. Furthermore, treatment with FO4 and FO5 activates mitochondrial membrane potential transition, an effect that has been reported to correlate with apoptosis activation.