The determination of elastic constants in isotropic solids by line focus acoustic (LFA) microscopy is discussed. A velocity corresponding to a global resonance of leaky Lamb waves has been obtained for different frequencies of excitation (f) from the V(z,f) curves. This fact is analysed by using a Kushibiki spectrum analysis. The elastic constants are determined from the comparison between measured and calculated velocities. The principle is based on the minimization of the summation of the square difference ∑|Vfc−Vfm|2 by using an algorithm based on the simplex method. This paper deals with the case of isotropic plates such as glass and aluminium plates. The influence of the initial values of cij on the final result is discussed in these cases. Experimental velocity profiles are measured on glass and aluminium plates as a function of the frequency varying from 8 to 17 MHz which corresponds to the bandwidth of the used transducer. The problem of geometric VG(z) and measured V(z) curves fitting is also discussed.