The invention relates to a process for cleaning in particular PCB-contaminated transformers and is characterised in that, after removal of the transformer liquid using an oil- or PCB-dissolving hydrocarbon solvent, a) the transformer is filled with the hydrocarbon solvent and it is exposed to an ultrasonic treatment and subsequently the hydrocarbon solvent containing the contaminating ingredients is removed from the transformer, and/or b) the hydrocarbon solvent brought into the gaseous state by heating in a vaporiser is passed into the emptied transformer and made to condense there and the condensate containing the contaminating constituents is discharged, these cleaning steps being carried out alternately or successively.
