During the 1970s and 1980s organophosphates (OPs), particularly monocrotophos (first tested 1969-70, registered 1972-73) and profenofos (first tested 1973-74, registered 1978-79), were the mainstay of mite control for the Australian cotton industry until propargite (first tested 1989-90, registered 1993-94) was released. Control problems with monocrotophos were reported as early as 1976 and NSW Agriculture has carried out a resistance monitoring program at Rydalmere since then. The results of those investigations are reported in this paper.