Hybrid stochastic and microcanonical algorithms are applied to simulate SU(3) lattice gauge theory with four species of dynamical, light quarks. Lattices of size 6×10 3 and bare quark masses ranging from m=0.250 down to 0.050 (in lattice units) are employed to study the character of the transition from hadronic matter to the quark-gluon plasma. Metasbability studies suggest that as the bare quark mass decreases the transition changes from strongly first order at m=0.250 to an abrupt crossover at m=0.050. The temperature of the crossover region is found to be T/Λ MS =2.14±0.10 and should be accessible to planned heavy ion experiments.