The purpose of the study was to discover the behaviour of painted wooden panels when subjected to rapid changes in ambient humidity. The reactions (in particular warping and shrinkage) of five samples when subjected to sudden hygrometric stresses were studied. The final experimental data led to a number of important observations on shrinkage and warping coefficients of painted wooden panels. In particular, the absolute necessity of spreading a protective substance on the backs of the panel paintings was stressed in order to ensure good conservation.