The influence of light, temperature and time of storage on the concentration of the anticoagulant agent ticlopidine in biological material was investigated. For this purpose, spiked blood samples as well as hair and nail samples from patients treated with ticlopidine were stored in glass containers at +25°C and +4°C. Half of them were stored in the absence of light by covering the containers with aluminium foil. The samples were analysed be fore storage, after 14 days and again after 60 days. For isolation of ticlopidine from biological material, a liquid-liquid extraction procedure with n-hexane was used, achieving an ex traction recovery of more than 80%. Ticlopidine determination was carried out by LC-ESI-MS. A statistically significant difference in ticlopidine concentration was observed in blood samples stored for 60 days with access of light at +25°C. No significant differences in ticlopidine concentrations were found in other analysed samples.