Conjunctival swabs taken from 40 cats with conjunctivitis and 65 cats without conjunctivitis were examined for the presence of Mycoplasma felis. The incidence of M. felis in cats with conjunctivitis was 25%. M. felis was not isolated from clinically normal cats. Inoculation of two isolates into the conjunctival sacs of healthy cats induced conjunctival hyperemia, starting 2-3 days after inoculation and disappearing without treatment within 7 days. It is concluded that M. felis plays a role in feline conjunctivitis.