Photodynamic diagnosis (PDD) is available at some centres. PDD makes cancer cells visible under violet light. This makes abnormal growths (tumours) easier to find and remove. More complete removal reduces the risk of cancer coming back. PDD is used in urology to test for bladder cancer. A catheter is inserted through the urethra and into the bladder. A solution of 5-aminolaevulinic acid or hexaminolaevulinic acid is passed through the catheter into the bladder. Then the catheter is taken out immediately. Cancer cells in the bladder process the chemicals in the solution and become fluorescent under violet light. No side-effects or complications have been reported for PDD.