468 severe aplastic anaemia (SAA) patients registered in the EBMT-SAA registry who did not undergo bone marrow transplantation and were treated with immunosuppressive therapy (IS; 96% of patients received ATG) were evaluated. Their median age was 23 years (range 1-73) at initial IS therapy, 59% were males; in 69% the aetiology of SAA was idiopathic. Of these 468 patients, 245 had a follow-up of less than 2 years after IS 166/245 died, 71/245 are still alive, 8/245 are lost to follow-up. Of 223 patients who survived greater than or equal to 2 years (LTS long-term survivors), 191 are alive, 21 died greater than 2 years and 11 are lost. Median follow-up of 223 LTS was 4.1 years (range 2.0-10.9). Comparison of 166 patients who died less than 2 years and 223 LTS revealed no difference at time of initial IS therapy as regards sex, duration of AA, or its aetiology, but the age distribution and, in particular, severity of SAA differed significantly: more LTS were between 21 and 40 years old (44% v. 32%, P less than 0.02), less LTS had reticulocytes less than 20 x 10(9)/l (63% v. 80%, P less than 0.001), polymorphonuclear granulocytes (PMN) less than 0.2 x 10(9)/l (30% v. 57%, P less than 0.001), haemorrhages (58% v. 79%, P less than 0.002) and infection (30% v. 49%, P less than 0.005) at time of IS. A gradual improvement of blood counts was seen in patients alive greater than or equal to 2 years after IS. At 2 years after IS 80% had a normal haemoglobin and PMN greater than 0.5 x 10(9)/l, but only after 5 years 80% of cases had platelets greater than 50 x 10(9)/l. Development of clonal disease was reported of 31 LTS: 19 developed paroxysmal nocturnal haemoglobinuria (PNH), one acute leukaemia, 11 myelodysplastic syndromes and of these 11 five subsequently acute leukaemia. The majority of these patients (23/31) are still alive. Actuarial mortality of LTS is 22% at 8 years, but so far no plateau was achieved. It is concluded that SAA patients who become LTS following IS, show an improvement in haematological status but are probably not cured and are prone to develop clonal (malignant) disease.