An empirical equation for the enthalpy of vaporization of quantum fluids is presented. Dimensionless analysis is used to define enthalpy of vaporization as a function of temperature with a standard deviation of about M. Experimental data represented in these variables show two different behaviours and exhibit different maximum values of the enthalpy of vaporization, one corresponding to fluids with a triple point and the other to fluids having a lambda point. None of the existing empirical equations are able to describe this fact. Also enthalpy of vaporization of helium-3, n-deuterium and n-tritium are estimated. (C) 2004 Elsevier B.V. All rights reserved.