Using the LEP 1 ALEPH data (1991-1995) the branching ratio BR( b → τν̄ τX ) is found to be (2.41±.21±.34)% using a missing energy technique. A complementary measurement using two leptons in the final state gives (3.94±.67 -56+.61)%. Combined together this leads to (2.58±.19±.33)%. The branching ratio BR( b → τν̄ τD ̇±X) is measured to be (0.94±.32±.37)% and the following limit is established: B - → τ -ν ̄ τ < .15% at 90% CL. BR( b → τν̄ τX ) and BR( B- → τ-ν̄ τ allow to set a constraint on the charged Higgs mass in the framework of any type 11 Higgs doublet model.