In a prospective study, 48 eyes with non-ischaemic and 35 with ischaemic central retinal vein occlusion (CRVO) were treated by isovolaemic haemodilution (IHD). Two or more cardiovascular risk factors were present in 42% of patients with non-ischaemic and in 69% of patients with ischaemic CRVO (p < 0.025). Nevertheless, IHD in no case caused serious cardiovascular complications. Minor problems were short fainting spells in 5% and a general weakness in 16% of the haemodiluted patients. The effect of IHD was measured by determining the time of maximal venous filling (tmvf) in fluorescein angiographies. Lowering the packed cell volume to 32–35% accelerated the tmvf from 18.4+1.61 to 13.1 ± 1.0 s (p < 0.001) in eyes with non-ischaemic CRVO and from 24.5 ± 1.2 to 14.8 ± 1.3 s (p < 0.001) in eyes with ischaemic CRVO. After 3 months, an increase in visual acuity had occurred in 27% of eyes with non-ischaemic CRVO and in 48.5% with ischaemic CRVO. These improvement rates could nearly be maintained after 1 year. 59% of eyes with non-ischaemic and 25% with ischaemic CRVO were able to read (visual acuity ≥6/15) after 1 year.