Solid Phase Microextraction (SPME) is used as a quick and easy alternative to standard distillation in essential oils composition assays. Due to the absence of the distillation step a considerable reduction of sample volume and of the time of sample preparation is possible. This method was used in experiments with essential oils obtained from Crithmum maritimum L. and Centella asiatica Urban (= Hydrocotyle asiatica L.). In this work the overground parts of Crithmum maritimum were analysed. The material was collected in 2003 from places of natural occurrence in Greece and Croatia, from a garden cultivation in Gdańsk, during the whole vegetation period, from plants from a control group and plants fertilised with Tytanit formula. Centella asiatica material was collected directly from an in vitro culture and from plants cultivated for six months in flowerpots, where they were transferred after five passages of in vitro culture. The analysis of components of monoterpene fraction was performed by gas chromatography. The percentage and composition of essential oils were different in all the tested samples. Crithmum maritimum material (from places of natural occurrence and from garden cultivation) shows the biggest differences in the content of a-pinene, 7-terpinene and sabinene. Plants treated with a Tytanit solution responded by increase of total percentage of essential oil with higher contents of 7-terpinene and sabinene. In Centella asiatica a higher percentage of essential oil (mainly a-pinene) was observed in roots than in leaves. Leaves treated with Ti ions had a higher amount of a-pinene than the control ones. Solid Phase Microextraction (SPME) method enables fast estimation of interference of each tested factor on the biosynthesis and composition of the essential oil. SPME was also useful in selection of the proper material for next experiments.