 In 1971, he conducted the Edmonton Symphony in a concert featuring the British rock band Procol Harum, which was recorded and released commercially as "," although due to an apparent distaste for rock music, from the start of the project Leonard disowned any association with the performance and went so far as to refuse to have his name listed in the credits.The concert and resulting recording went on to become the most successful live pairing of symphony orchestra and rock music to date and a worldwide best-seller, and even spawned a hit single, "Conquistador".In 1977, he arranged Mussorgsky’s "Pictures at an Exhibition" for piano and orchestra.