SU(2) lattice gauge theory with four flavors of quarks is simulated at nonzero chemical potential μ and temperature T and the results are compared to the predictions of Effective Lagrangians. Simulations on 169 lattices indicate that at zero T the theory experiences a second order phase transition to a diquark condensate state which is well described by mean field theory. Nonzero T and μ are studied on 12 3 × 6 lattices. For low T, increasing μ takes the system through a line of second order phase transitions to a diquark condensed phase. Increasing T at high μ, the system passes through a line of first order transitions from the diquark phase to the quark-gluon plasma phase.