The present study investigated the biochemical mechanism of abamectin resistance in a Tetranychus urticae Koch population collected from a bean greenhouse (BEYO 2) in Beyobasi village in Gazipasa district, Antalya province, and maintained in the laboratory. LC50' (60' 90) levels of BEYO 2 population of T. urticae were determined using a dry film method. The LC50 level of the BEYO 2 strain with abamectin was selected 15 times and was increased from 2.42 mu L 100 mL(-1) water to 38.67 mu L 100 mL(-1) water. A selected strain showing 35.05-fold resistance was named ABA 15 strain. It was investigated whether the resistant strain developed multiple resistance to different pesticide groups. The ABA 15 strain with abamectin resistance developed multiple resistance to chlorpyrifos, propargite, clofentezine, and fenpyroximate. The synergistic activity between abamectin and piperonyl butoxide (PBO), triphenyl phosphate (TPP), and S-benzyl-O,O-diisopropyl phosphorothioate (IBP) was studied in the resistant strain. Application of abamectin with synergists PBO, IBP, and TPP resulted in 1.76-, 2.43-, and 1.73-fold synergistic ratios, respectively, in the ABA 15 strain. The inheritance of resistance to abamectin of F I females after reciprocal crosses between resistant and Susceptible strains was maternal and paternal incompletely dominant. GSS (susceptible strain), BEYO 2, and ABA 15 strains were investigated in terms of the enzyme activities of esterase, glutathione S-transferase (GST), and monooxygenase (P450). No significant change was determined in esterase enzyme activities of the ABA 15 resistance strain to abamectin. The band density of esterase enzyme increased in the electrophoretic method. GST enzyme activity increased from 10.23 mOD min(-1) mg(-1) protein to 12.36 mOD min(-1) mg(-1) protein. The P450 enzyme activity was raised from 0.0017 mOD min(-1) mg(-1) protein to 0.0039 mOD min(-1) mg(-1) protein.