Recent investigations have suggested that Tycho did not die from urinary problems but instead from mercury poisoning—extremely toxic levels of it have been found in hairs from his moustache. This may have even been due to the various metals used to create his many different prosthetic noses that he wore. The results were, however, not conclusive. Prague City Hall approved a request by Danish scientists to exhume the remains in February 2010, and a team of Czech and Danish scientists from Aarhus University arrived in November 2010, to take bone, hair and clothing samples for analysis.

Some modern theories suggest that due to the discovery of the mercury in his body, it is possible he was intentionally or unintentionally poisoned. The two main suspects are his assistant, Johannes Kepler, whose motives would be to gain access to Brahe's laboratory and chemicals, and his cousin, Erik Brahe, at the order of friend-turned-enemy Christian IV due to rumors at the time that Tycho had had an affair with Christian's mother.

via Tycho Brahe - Wikipedia