The transmission of feline viral rhinotracheitis (FVR) virus was investigated. Virus could be successfully transmitted between shedding carrier cats and unrelated susceptible kittens, but only if there was intimate contact between them. Studies on the transmission of FVR virus from carrier queens to their kittens showed that although four of 10 queens shed virus in the post partum period, a total of only four kittens from three litters developed a contact infection. All four kittens remained asymptomatic. Two shed for one day only and did not become carriers (as evidenced by corticosteroid treatment) and two shed for 15 days and 25 days and were subsequently shown to have become carriers. None of the remaining kittens tested shed virus. There was no evidence of in utero transmission between FVR-recovered queens and kittens. Passive antibody titres in kittens born to FVR-recovered queens declined to less than 1 in 4 in individual animals by two to 10 weeks of age. Mean titres calculated from a linear regression equation reached less than 1 in 4 and less than 1 in 2 by six and nine weeks of age, respectively. Experiments using a multistage liquid impinger demonstrated that FVR virus was unlikely to be transmitted between cats by aerosol and this was confirmed by the ability of a sentinel cat to withstand virus shedding from carriers over a six month period, although housed in the same air space.