“…WJaLLnR et al (28) are of the opinion that the human cytomegaloviruses do not constitute a single serotype, and therefore, they, together with a few other investigators often use homologous strains (17,22,25) or a few laboratory strains (9,10,12,13,16,18,20,27,28) in the test systems. Others (6--8, 14, 23) including ourselves (1--5) have, however, had very good results using just one laboratory strain.…”