To determine whether chronic exposure to relatively loud noise has demonstrable biological effects in humans, a study was conducted on the effect of mother's exposure to airport noise while pregnant, and of social and biological characteristics of the family upon birthweight and gestation length. The sample of births was drawn from a community located adjacent to an international airport in the U.S., where noise levels had been measured previously. Mother's noise exposure was based upon noise levels near her residence in the community while she was pregnant. Data from 115 births were used, these being from mothers whose noise exposure history was most complete throughout the pregnancy. Using multivariate analysis to correct for family characteristics, the partial correlation coefficient for noise exposure and gestation length was negative, large, and significant in girls (r = -0.49, p less than 0.001). In boys the partial correlation coefficient was also negative but was smaller and did not quite reach statistical significance. Partial correlations with birthweight were smaller in both boys and girls and not significant. These results agree best with previous studies that suggest that noise may reduce prenatal growth. The size of the observed effects may be related to a conservative research design biased towards underestimation, as well as to the real effects of noise upon human prenatal growth.