Haemostatic changes in the loin pain and haematuria syndrome: secondary to renal vasospasm? Twenty-five patients (seven male, 18 female) were diagnosed as having the loin pain and haematuria syndrome. Presenting symptoms were either loin pain alone or pain associated with macroscopic or microscopic haematuria, and were longstanding, having been present for mean of 9.3 years in males, and 10 years in females. Ten patients described symptoms of passing gravel or renal stones but these were only demonstrated radiologically in two patients. Investigation of all patients showed anatomically normal renal tracts, normal renal function, and no significant proteinuria. Phase-contrast microscopy during episodes of haematuria revealed dysmorphic red cells in all 10 patients studied. Renal biopsies were performed in 20 patients and showed no glomerular pathology, but arteriolar and arterial hyalinosis was seen in 13 of 20 (65 per cent), fibro-elastosis in larger vessels in eight of 20 (40 per cent) and red blood cells in tubules in 13 of 20 (65 per cent) patients. The histological appearance in vessels was similar to that seen in cyclosporin A nephrotoxicity and would be consistent with the hypothesis that regional vasospasm occurs in the cortical circulation. Haematological studies in 22 patients, when compared with age and sex matched controls, showed the presence of circulating platelet aggregates, elevation of plasma beta-thromboglobulin (p less than 0.001), and increased platelet aggregation in response to serotonin and ADP (p less than 0.05 and p less than 0.03, respectively). Plasma concentrations of D dimer (p less than 0.02) and C-reactive protein (p less than 0.03) were also significantly elevated in the patient group. There was no deterioration of renal function during a mean observation period of 3.7 years and no patients developed proteinuria. Treatment was largely supportive; seven patients with intractable loin pain underwent surgical denervation with the relief of pain in four. 