  We estimate the most important corrections to the branching ratios for the
invisible decays of quarkonium states, arising from possible extensions of the
standard model. Among the possibilities considered are the presence of extra
Z-bosons, minimal supersymmetric extensions of the standard model with R-parity
violation, and decays into goldstinos. Prospects of detecting these corrections
at existing and future B-factories and tau-charm factories are discussed.
