A horizontal furnace system has been developed for growth by liquid-phase epitaxy of multilayer laser structures consisting of InP and (Ga, In) (As, P) incorporating a number of novel features. Double heterostructure lasers emitting at l.3μm with threshold current densities as low as 900 A/cm2have been made. Measurements of the far-field beam angles have allowed the dielectric constant step between the active quaternary and passive layers for lasers emitting at both 1.15 μm and 1.3 μm (im, to be deduced. Oxide-insulated stripe-geometry c.w. lasers, operating in a single longitudinal mode, have been made with threshold currents down to 180 mA