The photoexcited triplets in single crystals of the trans-stilbene-1,2,4,5-tetracyanobenzene (1:2) complex have been investigated by means of the ESR and DF ODMR techniques. The ESR lines attributed to localized species exhibit strong spin polarization whose dependence on the direction of the magnetic field has been examined. The zero-field splitting parameters have been measured: X = −308±15 MHz, Y = 2010±15 MHz, Z = −1702±15 MHz with the z axis directed along the normal to the t-stilbene phenyl rings. The negative sign of the DF ODMR signal has been attributed to annihilation of unlike triplets (exciton and X-trap), a process whose occurrence is supported also by decay measurements of the fluorescence.