Over the last several years bacteriophages (phages) related research became more interesting again. One of the reasons is the problem of antibiotic resistance that some bacteria has developed. Because of their natural ability for selective targeting to bacterial species or strains they represent a good therapeutic option in treatment of bacterial infections. Phage T4 specific targets E. coli and phage PC5 attacks C. jejuni. Phage adsorption involves reversible and irreversible interactions with host cells. Study of both phages reversible binding or desorption and speed of phage T4 adsorption was followed with free phages concentration and analyzed with »spot assay« method. Adsorption constant (adsorption speed) of T4 phage was 3,18 × 10-9 ml/min. We determined significant number of phage PC5 desorption which enabled analysis with Langmuir adsorption isotherm. It turns out that phage T4 binding on bacteria is much stronger and therefore we have not detected any desorption with 100-fold dilution in cold medium. We considered phage T4 reversible binding using different desorption media which could have an effect on different interaction types, like addition of 10 % ethanol and addition of 3 M NaCl. We also verified influence of ultrasonic treatment. We reached desorption of reversibly bonded phages in average concentration 1,98 × 104 PFU/ml with ethanol addition, (the number represent 0,17 % of initial phages), 3,25 × 103 PFU/ml with NaCl addition (0,02 % of initial phages) and 3,75 × 103 PFU/ml with ultrasonic treatment (0,04 % of initial phages). In all cases the percent of desorbed phages was extremely low, therefore we cannot absolutely talk about reversible desorption.