During recent years our research group has been engaged in biosynthetic studies dealing with antibiotics of two different sorts. In a continuing study we have investigated the biosynthetic origin of the very important aminocyclitol antibiotics, which include gentamicin, neomycin, streptomycin, spectinomycin, etc. This topic has been reviewed extensively within the past year (1, 2, 3). Concurrently, we have studied the biosynthetic origins of a number of antibiotics more of interest for their novel structural features than for their importance as clinically useful entities. It is a portion of the latter studies that will be described here. For each of the three antibiotics to be discussed—pactamycin, berninamycin, streptolydigin—two or more distinctly different biosynthetic routes appeared reasonable.