A prospective, randomized, cross-over study was performed to evaluate the safety and clinical efficacy of an immunoglobulin preparation for intravenous use (Intraglobin F) in comparison with the standard intra-muscular preparation. Twelve patients with idiopathic adult-onset panhypogammaglobulinaemia received intravenous Intraglobin F infusions of 300 mg/kg body weight every 4 weeks, or standard intramuscular injections of 25 mg/kg body weight every week (following a 4-week loading phase of 50 mg/kg/week) in random order for 24 weeks each with a 'washout' period between. At the end of this comparative trial eight of the patients received a further 24 weeks treatment with Intraglobin F at 300 mg/kg body weight every 3 weeks. Patients were assessed by diary cards, interview, laboratory screening (including assessment of serum opsonic capacity), chest and sinus radiographs, and full lung function tests. There were statistically significant, favourable changes in clinical parameters and trough serum IgG levels using the intravenous preparation but no other significant differences with respect to the two preparations. The eight patients who subsequently received the 3-weekly intravenous regimen improved further in these parameters, including serum IgG levels and serum opsonic capacity. Thirty per cent of infusions were associated with mild adverse reactions related to the rate of administration but one patient was withdrawn due to anaphylactoid reaction to her fifth infusion. Ten of the eleven remaining patients elected to continue intravenous therapy at the end of the trial. We conclude that Intraglobin F is preferable to the standard intramuscular preparations for control of idiopathic adult-onset panhypogammaglobulinaemia but that infusion intervals should be tailored to the individual's clinical response and results of appropriate functional in vitro assays, eg. opsonization.