WASHINGTON  Roger Clemens, in heated and sometimes indignant testimony, told a House oversight committee on Wednesday that his former teammate Andy Pettitte “misremembers” two conversations they had about human growth hormone, and that he was shocked to learn later that Mr. Pettitte had used the substance himself.

Mr. Clemens testified that in those conversations with Mr. Pettitte, he was talking about his wife’s use of H.G.H. one time and on another occasion was referring to something he saw on a television show. Mr. Clemens sought to rebut Mr. Pettitte’s sworn and damaging statements to the committee that Mr. Clemens told him point blank that he had used H.G.H.

But Henry A. Waxman, the California Democrat who chairs the committee, clearly did not believe Mr. Clemens, and pointed out that Mr. Pettitte’s wife, Laura, had also given an affidavit in which she confirmed that her husband told her about his conversation with Mr. Clemens shortly after it took place.

The account is crucial because Mr. Clemens, one of the most dominant pitchers of his era, gave a sworn deposition last week and testified under oath today that he never used H.G.H. or steroids.Another Congressman, Elijah E. Cummings, a Democrat of Maryland, pounded Mr. Clemens over the statements Mr. Pettitte made under oath and impugned his credibility.