A group of 25 patients with Stage II peripheral arterial occlusive disease was treated with pentoxifylline ('Trental' 400) for 90 days. Significant changes were observed during treatment in the haemorrheological parameters studied. At the end of treatment, reductions were found compared to basal values in blood viscosity (-10.1%), plasma viscosity (-9.5%), blood fibrinogen (-18.5%), and erythrocyte aggregation (-31.8%); blood filtrability was significantly increased (+41.0%). These positive changes in blood fluidity may be suggestive of beneficial influence of this drug on the clinical condition of claudicants.