The present article gives a summary of suspected adverse reactions reported by Swedish veterinarians during the period 1991-1995. The summary shows that severe adverse drug-reactions sometimes occur in Swedish veterinary practice. In horses, several cases of acute reactions in animals treated with procaine benzylpenicillin were reported and seven horses died within a few minutes after intramuscular injections of the drug. In cattle and swine most reports referred to the use of antimicrobial agents. In dogs reactions to vaccines were the most frequently reported adverse effects. The reactions were, however, usually rather mild. In dogs there were also several reports of severe reactions related to treatments with non-steroid anti-inflammatory drugs (NSAID) and alpha 2-receptor agonists. Amongst the reports six deaths were observed for each of these groups of drugs. In cats, as in dogs, adverse effects to vaccines were the most frequently reported reactions.