Hi there, If you mean what causes him not being able to urinate, then this could be due to him being unable to urinate from a few common reasons. The first is due to dehydration, which can be seen in patients undergoing chemo as they may be nauseated and not stay well hydrated. The second reason may be damage to his kidneys from the chemotherapy, which causes them not to work very well. This is more difficult to say without knowing the exact type of chemo, but gemcitabine is commonly use for gallbladder cancer and can cause nephrotoxicity (damage to the kidneys). The third reason could simply be to something obstructing (blocking) the urethra such as the prostate, which is very common in older men. If he hasn t urinated in three days, he likely needs hydration and a catheter inserted to monitor his urine output. I d encourage your friend to return to his doctor or the emergency room immediately. I hope this answers your question. Please feel free to contact me if you have any further questions.