ESDU 83036 is accompanied by a computer program (ESDUpac A8336) for estimating the lower natural frequencies of the initially unstressed plates. The calculation procedure is particularly applicable to fibre-reinforced composite laminated plates. Specially orthotropic plates are balanced laminates@ in which layers of equal thicknesses@ elastic properties and with the same orientation of their principal axes of orthotropy are symmetrically disposed about a central plane. A precise definition of this class of plates is given in ESDU 83035. The program uses a Rayleigh-Ritz analysis method to evaluate natural frequencies of flat plates having any combination of simply-supported and clamped edge conditions. An approximate graphical procedure is also provided for the estimation of the fundamental natural frequency of slightly curved laminated plates. Practical worked examples illustrate the use of the data.