The elastic resonance spectra of rectangular parallelepiped specimens of a polycrystalline sample and a pseudo-single crystal YBaCuO sample grown by the quench-melt-growth method have been measured. A new procedure which is based on the genetic algorithm has been applied for the determination of elastic moduli starting from the random sets of elastic moduli. The elastic moduli of polycrystalline YBaCuO specimen have been determined as follows: λ=0.46×1011 N/m2 and µ=0.46×1011 N/m2. They are much larger than the previously published data by Ledbetter, Austin, Kim and Lei. The determination of the elastic moduli of the pseudo-single crystal has not yet been completed.