The effect of vibration of 150 Hz frequency for three hours daily over three months on reproduction in female white rats was studied throughout the prenatal period and during the post-natal development of the offspring. The rats were exposed up to the time when fertilization occurred (first experimental group) and up to the end of the first quarter of pregnancy (the fifth day after fertilization) (second experimental group). In the second experimental group mortality before implantation was raised by a factor 1.5–1.8; in the first group the weight of the placenta was lower; and in both groups the weight of the foetuses was lower, and there was a higher proportion of foetuses with abnormal development of parenchymal organs and bones. On the 20th and 60th days after birth the offspring showed less motor activity. The data indicate that exposure to high frequency vibration before the onset of pregnancy and during the early part of pregnancy can have an adverse effect on reproduction.