The lungworm, Aelurostrongylus abstrusus, is a common parasite of the domestic cat in Great Britain and produces pulmonary lesions in that species which are occasionally severe. The disease may be reproduced experimentally either by the oral administration of third stage larvae which have been extracted from infected molluscs or by feeding the latter, themselves. For experimental purposes, the former procedure is preferred but the main disadvantage is that an infecting dose must be given on several occasions and over a period of days if sickness, with consequent loss of larvae, is to be avoided. Parenteral administration would, therefore, be advantageous. It is known that pulmonary infections have been produced in calves by the subcutaneous administration of larvae of Dictyocaulus viviparus (Wade and Swanson, 1958), in pigs by the intravenous and intratracheal injection of Metastrongylus spp. larvae (Kelley & Krous, 1961) and in sheep by the intravenous inoculation of Dictyocaulus filaria larvae (Michel and Sinclair, 1963). As neither intravenous nor intratracheal administration is particularly desirable in cats, it was resolved to attempt the reproduction of lungworm disease in that species by the subcutaneous injection of third stage larvae of Aelurostrongylus abstrusus.