A review of 34, 201 multigravid deliveries found 47 patients who had severe pre-eclampsia after previous normotensive, non-albuminuric pregnancies. In 13 of these patients the affected pregnancy was apparently by a new father compared with 3 matched controls (P less than 0.01). This evidence supports the idea of a paternal immunogenetic factor in pre-eclampsia; immunogenetics.