A capacitive balance that is able to work in the severe environment of a freeze-drying process has been conceived, constructed and tested. The influence of temperature variations had to be taken into account: a model of the instrument which makes use of the temperature of several components measured by three thermocouples was developed to correct the frequency signal generated by the device and to convert it into mass; the model parameters were identified by a least-squares method from blank lyophilisation runs. This balance offers the possibility of optimising the freeze-drying process through the accurate investigation of the process kinetics.