An ELISA for total herpes simplex virus (HSV) 1 antigen content and a test of immunogenicity based upon the female guinea-pig model of HSV 2 genital infection were applied to two samples from batches of HSV 1 subunit ('Skinner') vaccine. The ELISA was reproducible within an approximately threefold limit of error and batches 1 and 2 were indistinguishable in antigen content. The effects of vaccination in the guinea-pig model were assessed by a statistical analysis of scores derived from the principal clinical signs, vaginal oedema and lesions on the external genitalia. The statistical power of the guinea-pig assay was such that reductions in the severity of illness approaching 40% would be significant (P less than 0.05) on 90% of occasions. The ability to make quantitative estimates of immunogenicity will prove useful in the quality control of HSV vaccine batches which are destined for clinical trials in man.