In addition to the known diterpene casearin G (1), two new clerodane diterpene casearins type, casearin S (2) and casearin T (3), were isolated from an acetylated bioactive CH(2)Cl(2)/MeOH extract from leaves of Casearia sylvestris. The diterpenes 1-3 exhibited moderate but selective activity towards the DNA-repair deficient yeast Saccharomyces cerevisiae mutants RAD 52YK and RS 321. The structures of 1-3 were established on the basis of NMR spectroscopic experiments