After patent protection of original brand is over, there are a lot of generic products occurring on the pharmaceutical market. It may be the way to reduce the price, but on the other hand, one should expect the same quality and almost identity with original brand, because the development of generic drugs is based on pharmacological properties of the original brand. The aim of this study was to compare the similarity of two products with controlled release of felodipine--generic product Presid and original brand Plendil--which are commercially available in Czech Republic, based on in vitro dissolution testing. The dissolution test in three dissolution media of increasing pH (1.2, 4.5, and 6.5) for the simulation of physiological pH within the gastrointestinal tract confirmed controlled release of felodipine from the original product Plendil ER 5 mg and Plendil ER 10 mg during the period of 24 hours. The release of felodipine from generic products Presid 5 mg and Presid 10 mg was not controlled for 24 hours as it is indicated in the information leaflet. In the generic products, felodipine release was controlled just for 12 or 18 hours and in this respect did not show similarity with the original brand. Since patients take the drug just once a day in the morning, the controlled release of felodipine, which lasts only 12 to 18 hours, can cause insufficient blood pressure control especially in the most critical morning hours and higher cardiovascular risk.