Theoretical and experimental investigation of the pinch-effect–a compression of the electron-hole plasma by the selfmagnetic field of a current–has been performed for crystals of indium antimonide in which the plasma was produced by impact ionization. The emphasis was on the effect of surface recombination on the current-voltage characteristics of the crystal. The experimental results obtained for crystals with different surface recombination velocities give unambiguous evidence of the presence of a pinch-effect. Data of new experiments are given, which confirm the destruction of a pinched state by an external longitudinal magnetic field.