Treatment of shoots of the diploid female hop plant (Humulus lupu[us) with colchicine, with the aim of producing new varieties of seedless hops suitable for growing in New Zealand, has yielded two types of mutants. The one type are semi-sterile, carrying hops of normal size, and the other are highly fertile tetraploids bearing large hops. Crosses of both types of mutants with diploid male plants have produced a great number of practically sterile seedlings which are now being tested for their agronomic features and their brewing value. © 1969 Taylor & Francis Group, LLC. All rights reserved.