We studied the dynamics of serum human chorionic gonadotrophin (HCG) and its free alpha (HCG alpha) and beta (HCG beta) subunits in 49 early pregnancies achieved by in-vitro fertilization (IVF) and embryo transfer. Of the 49 early pregnancies, nine were normal singleton pregnancies, 11 were twin pregnancies, 11 were ectopic, eight ended in a clinical (spontaneous) abortion and 10 ended in a preclinical abortion. The HCG, HCG alpha and HCG beta concentrations in serum were measured on days 12, 19 and 26 after embryo transfer. Most ectopic pregnancies could be distinguished from singleton (and twin) pregnancies on the basis of low HCG concentrations by 12 days after embryo transfer, but clinical abortions could not be distinguished from singleton pregnancies. In general, the measurement of HCG alpha and HCG beta and the molar ratios of the various forms provided only marginal additional value to that obtained from HCG, but on days 19 and 26 after embryo transfer HCG alpha was the most sensitive indicator of a normal pregnancy after IVF and embryo transfer. We conclude that in ectopic pregnancies the concentrations of HCG, HCG alpha and HCG beta increase as expected but 1.5 days later than in normal pregnancies. This appears to be the result of a delay in implantation.