Tubulins extracted from the sporophytic developmental stages of Allomyces arbuscula have been characterised by one- and two-dimensional SDS-PAGE gels immunoblotted with monoclonal antibodies as α-, acetylated α- (Mr 57 kDa both) and β- (Mr 55 kDa) isoforms. The zoosporangial isoforms could be characterised only when precautions were taken to inhibit the strong tubulin proteolytic activity at this stage. The zoospores and zoosporangia contained greater amounts of the acetylated α- and β-isoforms than the mycelium, while the non acetylated α-isoform was present in greater quantity in the mycelium than in the zoospores or zoosporangia.