  A general method for reducing tensor form factors, that appear in one-loop
calculations in dimensional regularization, to scalar integrals is presented.
The method is an extension of the reduction scheme introduced by Passarino and
Veltman and is applicable in all regions of parameter space including those
where kinematic Gram determinant vanishes. New relations between the the form
factors that valid for vanishing Gram determinant play a key role in the
extended scheme.
