A convenient, sterile-filtered cocktail solution (1000X, in DMSO) containing four signaling inhibitors YPAC (Y-27632, a ROCK inhibitor, 10.0 mM; PD0325901, a MEK Inhibitor,1.0 mM; A83-01, a ALK5 inhibitor, 0.5 mM; and CHIR99021, a GSK-3β inhibitor, 3.0 mM), useful for maintaining the pluripotency of embryonic stem cells (ESCs).