  The extraction of the isovector s-wave pi N amplitude from pionic atoms is
studied with special emphasis on uncertainties and their dependence on the
assumptions made regarding the neutron density distributions in nuclei and on
the size of the data base used . Only `global' analyses of pionic-atom data
reveal a discrepancy between the extracted isovector s-wave pi N amplitude
b_1=-0.108\pm0.007 m_\pi^{-1} and its free pi N counterpart
b_1^{free}=-0.0885^{+0.0010}_{-0.0021} m_\pi ^{-1}, where the uncertainty in
the neutron densities is included in the error analysis. The role of `deeply
bound' pionic atom states is discussed and the reason for failure of these
states to provide new information is explained.
