Disclosed are pyrido�3,2,1-i,j!�3,1!benzoxazine compounds of the formula (I): ##STR1## wherein z represents a radical having the formula: ##STR2## wherein B represents --CH.sub.2 --, --O-- or a direct bond; and the other variables in formula (I) and Z are as described herein. The compounds have antibacterial properties and also disclosed are antibacterial compositions containing them and methods of using them to prevent or combat bacterial infections. Methods for preparing the compounds are also disclosed.