Editorial. Preface. Abstract. 1. Introduction. 2. Development of the embryo and fetus. 3. Biokinetic and dosimetric models. 4. Biokinetic data and models. Annex A: Transfer of alkaline Earth elements to the fetus. Annex B: Iodine biokinetics in the mother and fetus. Annex C: Decay products requiring Cf:Cm ratios and fetal distribution data. Annex D: Dose coefficients for workers.