A large number of elements in certain meteorites have isotopic composition different from that existing in rocks of the earth or the moon. Excess amounts of some isotopes, which are radiogenic daughters, are attributed to the in situ decay of their parent nuclide. Material containing radioactive parents is believed to have been injected into the condensing solar nebula, from astrophysical sites of their production shortly before formation of these grains. Other isotopic anomalies do not show

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... s dependent pattern which is characteristic of chemical fractionation. They must be primary isotopic abundances, if it is assumed that physico-chemical processes in the solar nebula cannot produce non-mass dependent fractionation. In such a case the observed isotopic ratios characterise elements differently synthesised and injected into the solar nebula which condensed before it had enough time to homogenise. Thus the isotopically anomalous matter has extra solar origin and may contain supernovae condensates, interstellar matter or dust from other stars. The evidence for different isotopic anomalies is briefly summarised and discussed in terms of the current ideas regarding chemical processes occurring in the early solar system.