The recent high prevalence of fatal bites by Brown snakes (Pseudonaja genus) has led to this study of venom yields from 66 brown snake milkings over 15 months. The amount of venom obtained from all species was higher than reported previously. Electrophoretic and Western blotting analyses of their venoms showed significantly lower avidity of Brown snake antivenom (BS-AV) for the prothrombin activator (PA) component (190 kD) than for other venom components, including the neurotoxins. The LD50 of P. inframacula has been determined for the first time.  SDS-PAGE (sodium dodecyl sulphate-polyacrylamide gel electrophoresis) and Western blotting studies have shown that the Pseudonaja venoms contained proportionately more PA component than venoms of the Taipan (Oxyuranus scutellatus) or the Fierce snake (O. microlepidotus). Neutralization of the prothrombin activator of the Common Brown snake (P. textilis) (Pt-PA) by BS-AV was found to be time dependent and 40% remained unneutralized after 30 minutes incubation.  Adult rats administered quantities of Pt-PA (IV) died with acute disseminated intravascular coagulation. Rats were made resistant to Pt-PA by preheparinization or by induction of tolerance to increasing quantities of Pt-PA. There is no evidence that Pt-PA has intrinsic toxicity apart from being a procoagulant. The improvement of BS-AV by addressing its deficiencies should be canvassed.