Tests on more than half the samples of German beansprouts suspected of causing an outbreak of E.coli in Europe have returned a negative result.
Of 40 samples from the farm being examined, 23 tested negative. Further tests are pending.
The agriculture ministry in the state of Lower Saxony says testing will continue but results will not be known in the short term.
Finding the cause of the outbreak may prove difficult, because weeks have passed since it began, it says.
The BBC reports a farm in Uelzen about 100km south of Hamburg was named on Sunday as the probable source of the bacteria that has killed 22 people.
The farm produces beansprouts including adzuki, alfalfa, broccoli, peas, lentils and mung beans, all grown in a nursery for consumption in salads.
General manager Klaus Verbeck was quoted by the Neue Osnabruecker Zeitung newspaper as saying that he could not see how it was to blame.
Initially, German officials pointed to Spanish cucumbers as the likely cause. More than 2000 people have fallen ill in a dozen countries and all had been travelling in northern Germany.
The European Commission is to hold a special meeting of EU farm ministers in Luxembourg on Tuesday.
Spanish farmers have seen a dramatic fall in exports and the government wants compensation from Germany or the European Union for the losses.