Samples of diarrhoeic shellfish poison (DSP) mussels from several parts of the Italian Adriatic coastline were extracted and tested according to a number of different methods presently available, i.e. Yasumoto's mouse biotest, Kat's biotest, the ELISA test and the HPLC method. Results were compared for toxic levels detected in each sample. While a common qualitative result (toxic/non-toxic) was given by all the methods, no clear quantitative agreement was found. The differences between methods and consequent lack of agreement in results are discussed.