By means of extensive equilibrium molecular dynamics simulations we have investigated the behavior of the interfacial tension gamma of two immiscible symmetrical Lennard-Jones fluids. This quantity is studied as function of reduced temperature T* = k( B) T/epsilon in the range 0.6 less than or equal to T* less than or equal to 3.0. We find that, unlike the monotonic decay obtained for the liquid-vapor interfacial tension, for the liquid-liquid interface, gamma(T) has a maximum at a specific temperature. We also investigate the effect that surfactantlike particles have on the thermodynamic as well as the structural properties of the liquid-liquid interface. It is found that g decays monotonically as the concentration of the surfactantlike particles increases.