The objective of this study was to find a reliable alternative to Freund's adjuvant in order to reduce the distress imposed on the animals without impairing the fusion efficiency for immune-positive clones. For this purpose several commercially available adjuvants and adjuvant formulations representing different classes of molecules were compared. Humoral responses and animals' distress evaluated by clinical assessment and histopathological examinations were investigated and compared to fusion efficiencies. In a first set of experiments seven adjuvants were tested essentially to determine their potential to induce distress. Poly(A).poly(U) and GERBU were selected for further investigations due to their low overall toxicity. They were combined with five different antigens and compared to the classic Freund's adjuvant system (CFA/IFA) and to control immunizations without adjuvant. The results showed that adjuvants of very low toxicity could induce a high fusion efficiency. According to a standardized immunization protocol, GERBU induced polyclonal titres similar to Freund's whereas animals treated with poly(A).poly(U) did not attain titres higher than mice immunized with antigen in saline. Poly(A).poly(U) however, exhibited the best fusion efficiency, Freund and GERBU were slightly less efficient. Therefore poly(A).poly(U) and GERBU may serve as valuable alternatives to Freund's adjuvant for generating monoclonal antibodies. Furthermore, these two adjuvants are very easy to use.