1. Seven male volunteers were given apomorphine (14–20 μg/kg) subcutaneously on a total of ten occasions. Nausea was experienced on six occasions and on four occasions there was no effect.
2. Venous samples were taken before injection, at peak nausea and 20 min later for assay of factor VIII coagulant activity (FVIIIC), von Willebrand factor antigen (vWFAg), the ristocetin cofactor (FVIIIRiCof), euglobulin clot lysis time (ECLT), fibrinopeptide A (FPA), FPA generation time, activated partial thromboplastin time (APTT), vasopressin (aVP) and adrenaline.
3. During nausea plasma aVP concentrations rose from median values of 0.4 pg/ml (at time 0) to 76 pg/ml at peak nausea and fell to 32 pg/ml 20 min later. Adrenaline rose from 0.36 to 0.91 nmol/l (P < 0.05) before falling to 0.55 nmol/l.
4. During nausea, FVIIIC rose from 100% to 143% (P < 0.05) and to 214% (P < 0.05) 20 min later. FVIIIRiCof and vWFAg showed similar changes. Plasminogen activator activity (106/ECLT2) rose from 23 units at time 0 to 592 units during nausea and 1135 units (P < 0.05) after 20 min.
5. The APTT fell from 49 s to 44 s during the study, plasma FPA levels and the FPA generation time both remained unchanged.
6. On the four occasions nausea was not experienced, there were no changes in vasopressin and catecholamine concentrations nor in haemostatic function.
7. During the study, plasma aVP concentrations rose to levels previously shown to influence haemostatic function. This provides further support for the view that aVP has a secondary role as a mediator of acute changes in haemostasis, and during nausea contributes with adrenaline to an abrupt change in factor VIII and fibrinolytic activator activity.