Based on sources, this article sums up the pioneering period of assertion of micro interval music, and Alois Haba's direct participation in the activities of the music avant-garde between the two World Wars. The article covers the period 1923-1946, and is extended by a brief supplement dealing with the post-war fate of Haba's experiment. The article is based mainly on material from Alois Haba's estate, deposited in the National Museum-Czech Music Museum, Prague, in which survives copious correspondence and other material, documenting this particular segment of the history of Czech modern music. Research focused on Haba's co-operation with the August Foerster piano-making firm from Loebau, in Saxony, who had a filial in Georgswalde (today's Jirikov), in Northern Bohemia, and, according to Haba's design, built several quarter-tone keyboard instruments. Supported by and in co-operation with this firm, Haba launched a number of promotional quartertone music concerts, where he was joined, in the role of pianist, by the composer Erwin Schulhoff.