Blebbistatin is a small molecule inhibitor discovered in a screen for inhibitors of nonmuscle myosin IIA. Blebbistatin is a specific inhibitor of nonmuscle myosin II, it inhibited contraction of the cleavage furrow without disrupting mitosis or contractile ring assembly. (+)-blebbistatin is an inactive enantiomer of (±)-Blebbistatin. (–)-blebbistatin is the active species, with an inhibitory concentration for 50% inhibition (IC50) of 2 uM, whereas (+)-blebbistatin is inactive. (+)-blebbistatin is useful as a negative control for the active enantiomer, (-)-Blebbistatin.