This article presents the first measurement of the
ratio of branching fractions B(Lambda0(b) --> Lambda+_c mu-
nu-bar _mu)/B(Lambda0(b) --> Lambda+_c pi+-). Measurements in
two control samples using the same technique, B(B-bar0 --> D+ mu-
nu-bar_mu)/B(B-bar0 --> D+ pi+-) and B(B-bar0 --> D*(2010)+ pi+-),
are also reported. The analysis uses data from an integrated luminosity
of approximately 172 pb-1 of p anti-p collisions at s**(1/2) ñ.96 TeV,
collected with the CDF II detector at the Fermilab Tevatron.