Haematuria frequency syndrome in patients with positive HIV serology: observations in Zambia. Observations are presented on 9 patients recently treated in the University Teaching Hospital, Lusaka, Zambia, for painful urinary frequency, suprapubic pain and microscopic and/or macroscopic haematuria without any demonstrable urinary tract infection. At cystoscopy the bladder mucosa of all patients depicted a highly characteristic, uniformly congested appearance with no demonstrable ulcers; there was no significant reduction in bladder capacity. The histological appearance was essentially non-specific in type with an apparent resemblance to that of interstitial cystitis; mast cells were, however, absent in all specimens. An important feature common to all patients was an associated HIV infection; cytochemistry of the bladder tissue did not reveal an associated cytomegalovirus cystitis. No such case was observed in Zambia prior to the advent of HIV infection and the phenomenon was observed only in seropositive patients. It has been suggested that the virus is likely to be associated with the genesis of the bladder symptoms. The natural history of the disorder, its incidence among the seropositive individuals and its pathogenesis remain unclear. 