In the 1950s and early 1960s Alexander Mackenzie was regarded as one of the most important of the St Ives group of UK artists - he was represented in London by Waddington Galleries [3 one-man exhibitions] and the prestigious Durlacher Bros. gallery in New York [2 one-man shows] who also represented Ben Nicholson, Barbara Hepworth and John Wells. 
Other St Ives artists showed at much smaller New York galleries: Peter Lanyon at Catherine Viviano and Patrick Heron & Terry Frost at Bertha Schaefer. 

He was not prolific as his quality control was remarkably good throughout his career - anything below standard was destroyed.

The new book below hopefully goes some way to show how good he is.