Certain novel 6-acylamino-2,2-dimethyl-3-(5-tetrazolyl)penam derivatives, and salts thereof; their use as broad-spectrum antibacterial agents; and methods for their preparation. Their preparation comprises acylation of the novel intermediate, 6-amino-2,2-dimethyl-3-(5-tetrazolyl)penam or simple derivatives thereof, followed, in some cases, by further transformations of the 6-acylamino group or by removal of a protecting group from the 5-tetrazolyl moiety. Process for the preparation of 6-amino-2,2-dimethyl-3-(5-tetrazolyl)penam, simple derivatives thereof and intermediates therefor.