The stabilities of transgene expression in pear clonal rootstock plants transformed by marker and commercial genes were evaluated. Nineteen transgenic lines expressing gus gene with and without intron were analysed over a period of 7 years (1999-2005) under greenhouse conditions and during 5 years (2001-2005) under field conditions. Fluorometric assays of GUS activity demonstrated differences between various lines but gene silencing was not observed in any line. Intron enhanced expression of the gus gene during all the years and in a stable manner. Histochemical assays showed transgene expression in floral organs, seed tissues and fruit flesh. Plants expressing the herbicide resistance bar gene demonstrated high levels of resistance to treatment with the herbicide Basta (active ingredient is phosphinotricin) at 20 L/ha dose (4-times the normal field dose) during two growing seasons with a three year interval. None of the transgenic plants showed any morphological abnormalities, in comparison with control non-transformed plants. The results confirm the possibility of stable transgene expression in fruit tree plants (Pyrus communis L.) after long-term cultivation in greenhouse and field.