Large free algebras in the ring of fractions of skew polynomial rings

It is shown that the division ring of quotients of a skew polynomial ring o f automorphism type, if infinite-dimensional over its centre k and satisfyi ng suitable hypotheses, contains the group algebra of a free group of large rank (usually at least \k\). The result applies, in particular, to the ske w polynomial rings constructed from rational function fields, and affirmati vely settles the conjectures of Makar-Limanov and Lichtman in this case.