This paper presents different quality parameters of the seeds of three cultivated medicinal plant species investigated: marshmallow (Althaea officinalis L.), flax (Linum usitatissimum L.) and fenugreek (Trigonella foenum graecum L.). For determination of agronomic and Pharmacopoeial parameters, different aged seeds, collected during six year period (2008 - 2013), were used. Flax seeds (Lini semen) and fenugreek seeds (Trigonellae foenugraeci semen) are considered as official herbal drugs, but not the marshmallow seeds (Althaeae semen). Following agronomic seed quality parameters were determined: germination energy, total germination, 1000-seed weight, and swelling index. The highest average germination parameters was recorded with fenugreek seed (EC = 97.7 % and UK = 97.8 %), quite lower were in flax seeds (EC = 75.2 % and UK = 80.7 %), while the lowest were in marshmallow seeds (EC = 8.1% and UK = 19.8%). 1000-seed weight of the flax and fenugreek were in agreement with previous research. The greatest average swelling index was achieved in flax seeds (6.5 ml), being higher by 38.5% in comparison to prescribed minimum (4 ml), while the average swelling index of fenugreek seeds was 6.2 ml, also exceeding the prescribed minimum, but slightly (6 ml). The average swelling index for marshmallow seeds was 5.4 ml. Although the Althaeae semen is not an officinal herbal drug, a six-year data on the swelling index of the seeds can be used as reference values in the further definition of a new Pharmacopoeial standard for this herbal drug.