Superconducting bulk YBa2Cu3O7-x (YBCO) material prepared by the melt growth method was characterized by AC susceptibility measurements. The measured susceptibilities were affected by the ac field amplitudes. The measured fundamental susceptibility was compared with the Bean model. An empirical function for the penetration field H (p)=H (alpha) (1-t) (beta) , where t is the reduced temperature, was obtained. Ac losses were determined at fixed temperatures and compared with theoretical calculations. A qualitative agreement was found between the experimental results and theoretical calculations.