Isolated platelet factor 3 (PF3) availability defect has been observed to be a common platelet functional disorder (PFD) in the Department of Haematology, All India Institute of Medical Sciences, New Delhi, India. One hundred and thirty-two patients were diagnosed to have this defect based on the presence of reduced PF3 availability, normal platelet aggregation with ADP, collagen, adrenaline, ristocetin, and arachidonic acid and normal PF3 content. PF3 availability was evaluated by measurement of Russel viper venom time (RVVT) on the patient's platelet-rich plasma (PRP) after incubation with ADP for 20 min. An RVVT value > 19.0 s was considered diagnostic of reduced PF3 availability in patients with normal prothrombin and activated partial thromboplastin times. Isolated PF3 availability defect occurred in patients with ages between 2 and 65 yr and had a female preponderance (M:F = 1:2). One fifth of the patients had a positive family history of similar mild bleeding diathesis, indicating an autosomal dominant pattern of inheritance. All patients presented with mild bleeding manifestations, the commonest symptom being appearance of recurrent ecchymotic spots. In females, menorrhagia was the commonest symptom. A pilot study was conducted on 45 patients to evaluate the therapeutic role of oral soya bean (50 g/d). The clinical response was evaluated after 3 months. Soya therapy resulted in disappearance of bleeding problems in 5 patients and reduction in frequency and severity of bleeding in 26 patients. A repeat PF3 availability test after 3 months of therapy showed complete correction in 4 and partial correction in 12 patients. It is evident from McNemer's test that both the clinical and the laboratory parameters (PF3 availability) showed a similar response to soya therapy (p>0.05). Pre-soya therapy mean PF3 availability values differ significantly from those after soyatherapy (p<0.01). Thus, soya bean appears to have a therapeutic potential in isolated PF3 availability defect.