In an open study, 21 patients suffering from chronic non-seasonal rhinitis and allergic to house mites (HDM) have been treated for 1 year with either a new extract (Pharmalagen; n = 10) or an allergoid, pyridine denatured, extract (Alavac; n = 11), both precipitated with AlOH3 (depot). The following investigations were performed before and after therapy: clinical scoring (for 4 weeks), quantified skin prick tests (SPT) and nasal provocation tests (NPT) with HDM, and determination in serum of HDM-specific IgE and IgG. Both groups were compared with six patients who remained untreated and underwent the same investigations. Hyposensitization with either extract induced an improvement in clinical scores (P less than 0.05), a decrease in SPT reactivity (Pharmalgen: P less than 0.001; Alavac: P less than 0.01), a marked increase in the nasal tolerance to HDM (P less than 0.001) and in HDM-specific IgG (P less than 0.001). In the group of untreated patients, all these parameters remained unchanged. Compared with the Alavac extract, the Pharmalgen extract was more active in decreasing SPT reactions (P less than 0.05) and inducing a HDM-specific IgG rise (P less than 0.05). Although both extracts induced some untoward allergic reactions, no adrenaline was used at any time during the study. These data suggest that hyposensitization with depot extracts of HDM can be considered a safe and active adjunct to the treatment of allergic rhinitis.