Pharmacokinetics of clonidine were examined in ten women during pregnancy, in nine during nursing, and in the newborns of these women. Clonidine crosses the placenta easily, and its concentrations were equal in maternal serum and umbilical cord serum. Amniotic fluid concentrations were up to four times that found in serum. Clonidine concentrations in milk were roughly twice that in maternal serum; in the serum of the newborns the concentrations were about half those of the mothers. All concentrations corresponded well to the doses of the drug. The neurologic examinations and assessments of serum electrolytes and blood glucose showed results parallel with those of newborns of nontreated mothers.