Positive Paul-Bunnell-Davidsohn reactions in sera from healthy individuals, usually blood donors (where the incidence may be 0-9 to 1 6%), have been described on several occasions (Barratt, 1941;Hobson, Lawson, and Wigfield, 1958;Virtanen, 1962). The significance of these observations is obscure and whether such heterophile antibodies represent subclinical infectious mononucleosis or are chance findings, to be dismissed as 'false-positive reactions', is not clear. The association of the EB virus with infectious mononucleosis (Henle, Henle, and Diehl, 1968;Evans, Niederman, and McCollum, 1968) sheds some light upon this problem, for the high incidence of antibodies to this virus in the community showed that asymptomatic infection with the probable causative agent of infectious mononucleosis was widespread. Holborow, Hemsted, and Mead (1973) have recently observed that a high proportion of patients with active infectious mononucleosis possessed antibodies to smooth muscle. Our own unpublished data support this observation but we were surprised that some of our control medical students and nurses also had smooth muscle antibodies. These antibodies are usually found in patients with some degree of liver damage (Johnson, Holborow, and Glynn, 1965) but our medical students and nurses were, apparently, quite healthy. Their sera were therefore tested for EB virus antibodies and, in the following report, we outline our findings and suggest that subclinical EB virus infection, associated with the development of smooth muscle antibodies, may be not uncommon in young adults.
