In two independent trials 10 and 12 healthy volunteers received the novel intravenous immunoglobulin (IVIG) preparations BT 511 and BT 507, respectively. BT 511 contains 5 g human plasma proteins per 100 ml, more than 95% of which are immunoglobulins of the G class (IgG). BT 507 contains in addition 61 IU antibody against hepatitis B surface antigen (anti-HBs).ml-1. In trial I volunteers received 4.0 ml/kg (n = 4) and 8.0 ml.kg-1 (n = 6) BT 511 to study the tolerability and the magnitude of the increase in immunoglobulins in plasma as well as their decline over 1 month. After administration of the lower dose, plasma IgG increased from 10.7 to 14.7 g.l-1 directly after the infusion. Following the 8.0 ml.kg-1 dose a more pronounced increase from 12.4 to 21.2 g.l-1 was observed. No adverse events occurred. After 1 month IgG concentrations had almost reached baseline values at 12.2 g.l-1 in the 4.0 ml.kg-1 group, but were still significantly increased at 15.2 g.l-1 after the high dose. There was a linear correlation between the maximal IgG plasma concentration and the subsequent decline of IgG during the 29-day observation period. After administration of BT 507 maximal anti-HBs concentrations of 1778 mU.ml-1 occurred 1.4 h after termination of the infusion. The terminal elimination half-life was 22.4 days, and total clearance and volume of distribution were determined to be 0.122 ml.min-1 and 5.41, respectively. The pharmacokinetic parameters calculated for anti-HBs as an indicator of IgG were in accordance with the pharmacokinetic behaviour of native IgG.