A South American rattlesnake bite without clinical manifestations of envenoming (termed 'dry-bite') has not been recognized to occur by the Brazilian Ministry of Health, which recommends the administration of antivenom to all bitten patients. During 36months of an observational study on South American rattlesnake bites in Minas Gerais, Brazil, 12% of 41 patients with fang marks at the bite-site did not present clinical or laboratory features of envenoming and had no plasma venom detected before specific serotherapy, fulfilling the criteria for the diagnosis of true 'dry-bite'. Data from these preliminary observations suggest that these patients should be correctly diagnosed since they should not be treated with unnecessary and sometimes hazardous and expensive serotherapy. Copyright (C) 1998 Elsevier Science Ltd.