Energy levels E(0.42eV), H(0.61eV), E(0.66eV) and H(0.69eV) are introduced by the existence of the 4d transition impurities Mo and Pd, respectively, in GaAs. Based on the optical-electric behavior of transition impurities Mo and Pd in GaAs, it is suggested that these impurities do not act as effective recombination centers in GaAs.