A He-Ne laser has been employed in the determination of etched track parameters in glass and plastic solid state nuclear track detectors. The Fraunhofer diffraction pattern was analysed by using a photecell arrangement. A fairly good agreement has been observed in the track parametric values as obtained by the laser diffraction method and by the direct optical microscopic measurements. The results show that although the best use of the technique is to analyse round shaped deep etch pits, fairly accurate estimations can be made even for shallow and randomly orientated etch pits (such as these produced by low ionising particles detected in 2π-geometry).