Coccidia infections occurring in cats (Isospora, Cryptosporidium, Toxoplasma, Hammondia, Sarcocystis), peculiarities of their life cycles, and diagnostic, prophylactic and therapeutic possibilities are described; the problems of Toxoplasma infections of cats are intensively discussed. If the oocystshedding cat is suspected to be the source of infection for the owner, only both coproscopical and serological results allow an appropriate advice.