The penetration of 50- to 60-Hz electric fields into the membrane and interior of a long nerve or muscle cell is investigated analytically when the incident electric field is perpendicular to the length of the cell. Explicit formulas are derived for the induced electric fields in the interior and in the membrane. It is shown that these are comparable to those in a spherical cell with the same radius; that is, the induced transverse electric field in the interior of the long cell is very small. The induced voltage across the membrane is also determined. These results supplement earlier ones which showed that when the incident electric field is parallel to the length of the cell, the electric field induced in the axon and membrane is the same as the incident field and that there is no voltage induced across the membrane. The combination of the induced axial and transverse electric fields provides a complete picture of the induced electric field in both the membrane and the interior of a long cell in an arbitrarily incident electric field. ¿ 2000 American Geophysical Union