The cause of uveitis is frequently obscure. When conditions such as syphilis, gonorrhoea, sarcoidosis, tuberculosis, toxoplasmosis, brucellosis, and diabetes mellitus have been excluded, it has usually to be admitted that in the majority the aetiology is unknown. The occurrence of uveitis in association with genital infection has been recognized for a long time. Most of the literature deals with uveitis as a complication of gonococcal infections in males. Woods (1956) states that patients with chronic gonococcal infection of the genito-urinary tract, or with gonococcal arthritis, may develop violent, acute attacks of non-granulomatous iritis, and he considers that this is most likely to be due to a hypersensitivity phenomenon. Much less attention has been devoted to its association with "non-specific" genital infection.King, Williams, Nicol, and Loudon (1946) and Harkness (1950) describe iritis as one of the complications of non-gonococcal urethritis. Ford (1953) found six of his 21 patients with Reiter's disease to have relapsing iritis. The association of iritis with ankylosing spondylitis is well known (Birkbeck, Buckler, Mason, and Tegner, 1951). Romanus (1953) examined 117 men with ankylosing spondylitis and found that iritis had occurred in 33 of them. His findings led him to the conclusion that the majority of cases were due to urogenital infection, mainly prostato-vesiculitis.The aetiology of non-specific genital infection is unknown. Organisms such as streptococci, staphylococci, and diphtheroids are frequently found in the urethral secretions of patients with "non-specific" urethritis and in the prostatic fluid of patients with chronic prostatitis. These organisms are, however, usually regarded as commensals. (Whittington, 1957), is rarely found in the prostatic fluid. The causes of non-specific genital infection must therefore await further investigations and new discoveries.The object of this communication is to give a preliminary description of an investigation which is being carried out at the Institute of Ophthalmology into the possible association of "non-specific" genital infection and uveitis. In the period of 7 months from May to December, 1957, 85 patients attending the Institute were fully investigated. During this period all new male patients attending for the first time with uveitis, whether anterior or posterior, were investigated, thus eliminating the possibility of selection. Each patient was closely questioned as to clinical history and a thorough physical examination was performed. Specimens of prostatic fluid were obtained by prostatic massage and collected on five slides which were at once examined microscopically. A stained smear of the prostatic fluid was also examined. Culture plates containing medium for growing pleuropneumonialike organisms and plates for anaerobic and aerobic cultures were inoculated with prostatic fluid. The centrifuged deposit of urine was inoculated on to culture medium for P.P.L.O. and a stained smear of the deposit was also examined microscopically. D...