CIPR immediate past president Lionel Zetter and PRCA public affairs committee chair Rod Cartwright were summoned to appear before the public administration committee this week.
Association of Professional Political Consultants (APPC) chair Gill Morris also gave evidence as the committee pressed ahead with an inquiry into the transparency of the lobbying industry.
Morris told the MP: 'I'm proud to be a lobbyist.'
Zetter said: 'We are convinced that the industry is cleaner than it has ever been.'
Meanwhile, Cartwright claimed that the PRCA's set-up 'makes it clear who is paying for lobbying' - an assertion that went unchallenged by the committee.
Members of the select committee appeared to have different takes on the public affairs industry.
Labour MP Paul Flynn laid in to the lobbyists, claiming: 'You give advantage to the already advantaged.'
But Tory Charles Walker said there was still scant evidence of lobbyists behaving improperly. 'We haven't found any smoking guns,' he said.
Committee chair Tony Wright, one of the best informed MPs on this subject, was not present at the session.