Abstract Examination of glutaraldehyde-treated collagen-based vascular prostheses by immunofluorescence methods indicated that a high degree of autofluorescence was present. This background autofluorescence, which resulted from the glutaraldehyde used in the manufacture of the prostheses, made it very difficult to visualise specific antibody-associated fluorescence. The use of different fluorochromes with a variety of filter blocks did not lead to acceptable conditions, since the autofluorescence showed a broad emission spectrum at various excitation wavelengths. An alternative which proved satisfactory was the use of quenching agents. In particular, 1% Evans Blue led to a shift in the autofluorescent spectrum to longer wavelengths. Specific monoclonal antibody detection of collagen was then possible, with the use of additional filters to mask out the longer autofluorescence wavelengths.