Forty three children with newly diagnosed idiopathic thrombocytopenic purpura (ITP), platelet count (pl.c.) below 20 x 10(9)/l, and either clinically significant bleeding or failure to show a spontaneous platelet rise within three days of admission were randomly allocated to treatment with intravenous infusions of either immunoglobulin (IVIG) 1 g/kg or methylprednisolone (MPPT) 30 mg/kg on two consecutive days. Prompt induction of partial remission with pl.c. > 50 x 10(9)/l after 72 hours was seen in 21/23 given IVIG versus 10/20 given MPPT (exact p = 0.003); mean pl.c.s after 72 hours were 188 versus 77 x 10(9)/l (2p < 0.001). Poor responders were then given the alternative infusions in addition. After six days, complete remission with pl.c. > 150 x 10(9)/l was achieved in 16/23 versus 10/20 (p = 0.16). During six months follow-up, there were no significant differences regarding relapse rates or chronic course. Eleven children with relapse were crossed over to the alternative treatment arm: the estimated treatment effect in pl.c. after 72 hours was 134 x 10(9)/l in favour of IVIG. These results indicate that IVIG infusions may be preferable to high-dose corticosteroids as initial treatment for children with ITP.