The Giotto frescoes of the Scrovegni Chapel in Padua are among the best preserved of Italy. However, they have shown deterioration which can be classified in three categories: 1) Pulverisation due to decay of <i>a secca tempera medium and treatment of past centuries. 2) Scaling where previous restorers have applied a fixative, probably casein or egg, and where tempera was painted on <i>buon fresco. 3) Deterioration of the calcium carbonate due to water seepage and other attacks. The paper discusses the scientific investigations made on these frescoes.