  We have compared the frequency of high-redshift Hydrogen HI 21 cm absorption
with that of associated molecular absorption in two quasars to place new (1
sigma) upper limits on any variation in y = g_p.alpha^2 (where alpha is the
fine structure constant and g_p is the proton g-factor) of |Delta(y)/y| <
5.10^{-6} at redshifts z=0.25 and z=0.68.
