The determination of the isothermal variation of the entropy (ΔS T ) is discussed in the present work. We show that ΔS T has very different profiles and magnitudes when calculated from M vs. H or M vs. T experimental data. For MnAs compound, ΔS T obtained from M vs. T data does not present a colossal peak. This result and the agreement between theoretical and experimental non-colossal magnetocaloric effect indicate that the colossal peak may be miscalculated from M vs. H experimental data. For Gd 5 Ge 2 Si 2 compound, ΔS T obtained from M vs. T data does not present the peak observed in ΔS T from M vs. H data.