Bromosporine is a broad spectrum inhibitor for bromodomains with IC50 of 0.41 μM, 0.29 μM, 0.122 μM and 0.017 μM for BRD2, BRD4, BRD9 and CECR2, respectively. In cell-based assays, Bromosporine (1 μM) accelerates FRAP recovery of BRD4 and CREBBP, while shows no activities against TIF1α, BAZ2A, and SMARCA2 (at 10 μM). Bromosporine shows moderate cytotoxicity in HeLa cells at 18 μM. It is a very useful chemical probe for bromodomain functional assays.