UVA light-induced DNA single strand cleavage by a set of 12 monomethyl substituted benz [a] anthracenes (MBAs) along with their parent compound, benz [a] anthracene (BA), and the potent carcinogen, 7, 12-dimethylbenz [a] anthracene (DMBA), was studied. On the basis of the relative DNA single strand photocleavage efficiency of the fourteen compounds, they are divided into three groups:(1) strong DNA cleavers, 4-MBA, 5-MBA, 6-MBA, 8-MBA, 9-MBA, ...