The effect of oxpentifylline on mental state of patients suffering from primary degenerative dementia (PDD) and multi-infarct dementia (MID) was investigated in a double-blind study. After an initial 2-weeks washout period, the patients were randomly selected to receive either 400 mg oxpentifylline thrice daily or matched placebo tablets for 12 weeks. Eighteen male and 18 female patients aged 60-88 years were included but 5 patients dropped out during the first 2 weeks of the trial due to poor motivation. Two patients for non compliance and one for protocol violation were further excluded from final analysis. The age and sex distribution of the patients receiving placebo were comparable to those of treated patients. The mean pre-entry severity of dementia, as assessed by Folstein's mini mental state (FMMS) and Sandoz Clinical Assessment Geriatric Scale (SCAGS), was greater in the latter group (p less than 0.05). Although both groups showed slight improvement at the end of 12 weeks' treatment, no significant drug-related progress was observed. However, the MID patients (n = 4) who received oxpentifylline showed greater improvement (p less than 0.05) than the MID patients (n = 7) who were treated with placebo. No such benefit was observed in oxpentifylline-treated PDD patients. It is, therefore, suggested, that oxpentifylline (a haemorrheological agent), is probably beneficial only in MID patients, but further long-term studies involving a larger number of patients are required.