Placental tissue from 160 abortions provoked during the 6th--12th weeks, and 109 spontaneous abortions between weeks 5 and 16, were studied histopathologically on respect of a comparison and quantitation of hydrop degeneration. Significantly more cases of severe hydrop degeneration were observed among the spontaneous abortions (p < 0.001). Of these abortions, 87 per cent were hydrop degenerated to varying degrees; 41 per cent were severely hydrop degenerated. Among the provoked abortions, approximately 81 per cent were hydrop degenerated to varying degrees but only 6.9 per cent were severely hydrop degenerated. The relationship between severe hydrop degeneration and chromosome abnormality is discussed.