The last undisputed (among Catholics) infallible statement was Pope Pius XII's 1950 definition of the Assumption of Mary into Heaven. (See http://www.thenazareneway.com/papal_infallibility.htm.) For a discussion of the ex cathedra status of Humanae Vitae that contains more background than you'll ever want on infallibility, see http://www.rtforum.org/lt/lt43.html.
-- Jim Cullen
>
>The last "ex cathedra" pronouncement from the Vatican that I know of
>was in the sixties. It was an encyclical teaching against
>contraceptive use. There is some argument within the church about
>this because it is a stupid teaching and eventually they will find a
>way to finesse their way around it. Nothing the current pontiff said
>in his speech concerning Cuba would qualify as infallible.
>An interesting aspect about infallibility is that the "list" of
>qualifications for infallibility was not issued either "ex cathedra"
>or even as an Authentic Magesterium (this is disputed by some) so in
>essence the list is non-infallible and subject to revision.
>The comment was also posted that catholics would be uncomfortable
>with the characterization of the pope as "gods representative on
>earth". When issuing "ex cathedra" pronouncements via encyclical
>letter or some such other contrivance the pope is referred to as the
>"vicar of christ" but some popes used "vicar of god" which is
>basically the same as saying "substitute for christ". More than a
>mere representative they believe themselves an actual substitute!
>