The relationship between the vitamin B6 status of 180 pregnant women and the incidence and degree of morning sickness experienced during the first trimester was investigated. There were no significant differences in plasma pyridoxal 5'-phosphate (PLP), erythrocyte aspartate aminotransferase (AspAT) activity, and stimulation of erythrocyte AspAT activity by exogenous PLP between subjects who experienced morning sickness and those who did not. No relationship was found between these indicators of vitamin B6 status and the degree of morning sickness experienced by this group during early pregnancy. There were no differences in the number of women who experienced morning sickness or in the number with different degrees of sickness when plasma levels of PLP, erythrocyte AspAT activity or stimulation by PLP were divided into upper and lower 50th percentile groups and compared. Therefore these data show no relationship between vitamin B6 status and the incidence or degree of morning sickness.