The aim of the research was to identify characters which determine the yield and the content of silymarin in the fruits (achenes) of Silybum marianum as well as to show the range of their variation. The research was performed based on field experiments conducted at the Mochełek Research Station (53^o13’ N; 17^o51’ E) over 2003-2005. Fruit yield and the content of silymarin were affected mainly by weather conditions, the forecrop and the sowing time. The coefficient of variance for fruit yields was 37.3%, and the content of silymarin – 12.7%. Plant height prior to harvest, number of fruits per anthodium on lateral and main shoots, thousand fruit weight, number of anthodiums with pappus and number of all the anthodiums per plant were significantly correlated with fruit yield. The content of silymarin was positively correlated with the number of plants per m² prior to harvest, plant height prior to harvest and fruit yield, and negatively correlated with the content of total N in the reserve material of fruits. The content of flavonolignans which make up the silymarin appeared relatively constant and only silydianin changes slightly more than the content of silychristin and isosilybin.

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