Purple colouring of the urin bag in a patient with infection of the urinary tract, probably with Pseudomonas (could not be proven). The reason for the purple colour could not be ascertained so far. It is thought to be connected to the conversion of indican in the urin to indigo blue. Bacteria are speculated to play a role in most cases. The purple colour is thought to be due to agglomeration of pigments to the urin bag itself. Others regard the mixing of two pigments, indigo blue and indigo red, to be the cause for the purple colour. After oral antibiotic treatment, the urin cleared and a new urin bag did not discolour again.