The effects of natural fermentation upon the lectin in the seeds of Lens culinaris cultivar Magda 20 were investigated. Suspensions of lentil flour were allowed to ferment naturally at different lentil flour concentrations (79, 150 and 221 g l -1 ) and temperatures (28, 35 and 42°C). During fermentation, samples were taken at daily intervals (0, 24, 48, 72, and 96 h) and lentil lectin activity was measured by haemagglutination test. With the progress of fermentation there was a rapid decline in haemagglutination activity in all the batches. The largest decrease occurred between 0 h and 24 h of fermentation in all the conditions. The lectin concentration showed the maximum reduction at 72 and 96 h, under the fermentation conditions of 79 g l- 1 and 42°C, when the initial lectin content measured by ELISA was reduced by 98 and 97.8%, respectively. The changes in lentil lectin were also followed by SDS-polyacrylamide gel electrophoresis and immunoblotting. The results confirmed those obtained by ELISA and indicated that the lectin almost disappeared after 72 h of natural fermentation under the optimum conditions of flour concentration and temperature.