Аннотация:We investigate the variability of physical parameters in the Broad Line Region (BLR) of NGC 5548 using the Boltzmann plot (BP) method. We apply the method on the Balmer lines observed from 1996 to 2004, and find that variability earlier detected in the lines, is also present in the temperature. We find that the average temperature for the considered period was T~10000 K, and that varies from 6000 K (in 2002) to 15000 K (in 1998). This variation correlates with the optical continuum intensity (r=0.85) and may indicate the existence of an accretion disc in the BLR of NGC 5548. Additionally, we use the CLOUDY code to discuss the obtained temperature.