All spontaneous reports to the manufacturer and to WHO's database INTDIS regarding adverse reactions to clinical dextran after preinjection of dextran 1 and to dextran 1 alone 1983-1991 were collected. During 1983-1991 a total of 4.8 million doses of Promit were sold in fourteen countries. The incidence of severe DIAR (grades III-V) to clinical dextran after the prophylactic use of hapten inhibition was approximately one case per 200,000 doses of dextran 1. In Sweden, where reporting of severe adverse drug reactions is mandatory, the incidence was one case per 70,000. This indicates a 35-fold reduction in the incidence of severe DIAR compared with the use of clinical dextran without dextran 1. Only two fatal reactions were reported; the incidence was therefore one case per 2.4 million doses, indicating a 77-fold reduction. Both these occurred in patients with extremely high titers of DRA. Side effects to dextran 1, mostly mild, were reported in one case per 100,000 doses. These side effects were not antibody mediated. It is concluded that the introduction of hapten inhibition with dextran 1 has greatly reduced the risk for serious side effects to dextran, making dextran one of the safest colloids in use.