In order to examine allelopathic effect of Cannabis sativa L. on germination capability and seedling growth of Lactuca sativa L., a study was performed in laboratory conditions. Treatments were set up in randomised block design in four replications for each of four concentration ranges of 25, 50, 75 and 100 % of aqueous extract made of shoot parts and 4 identical extract concentrations made of root of cannabis. Control variant was lettuce seed treated by distilled water. During the studies shoot and seminal root length of lettuce seedlings were measured after treatments with different concentrations of extracts made of root and shoot parts of cannabis, and the obtained values were compared with the control. The obtained results suggest that the extract from the shoot parts of cannabis in high concentrations of 75 and 100% had inhibiting effect to the germination indices while the extract from the root had no statistically significant effect on germination of lettuce seeds. Extract made of root part of cannabis showed also stimulatory effect to shoot and seminal root length of lettuce seedlings in extract concentrations of 50, 75 and 100 %. V laboratorijskih razmerah je bil preučevan alelopatičen učinek navadne konoplje (Cannabis sativa L.) na kalitev semen in rast kalic vrtne solate (Lactuca sativa L.). Obravnavanja so bila izvedena kot naključni bločni poskus v štirih ponovitvah z vsako od štirih koncentracij, 25, 50, 75 in100 %, vodnega izvlečka poganjkov in korenin konoplje. V kontrolnem poskusu so bila semena vrtne solate tretirana na enak način z distilirano vodo. Poleg indeksa kalitve sta bili v poskusi merjeni še dolžina poganjkov in semenskih korenin kaleče solate. Rezultati so pokazali, da je imel izvleček poganjkov konoplje v večjih koncentracijah, 75 in 100 %, inhibitorni učinek na kalitveni indeks, medtemko izvlečki iz korenin niso imeli statistično značilnega vpliva na iste merjene parametre. Izvleček iz korenin konoplje je imel stimulativni učinek na dolžino poganjkov in semenskih korenin vrtne solate pri koncentracijah 50, 75 in 100 %.