1-(m-Methoxyphenyl)-2-(dimethylaminomethyl)-cyclohexan-1-ol (L 201) was split into the cis- and trans-isomers and the conformations of the two isomers were determined by 13C-NMR-spectroscopy. Molecule models showed that both conformeres were similar to the geometrical structure of morphine. The adaptation of the morphine structure was better with the more active trans-isomer than with the cis-isomer. Tramadol, the trans-isomer, was separated into its optical antipodes. When tested for analgesia in the electro-stimulation test with mice, all compounds showed analgetic activity. The trans-isomer was more active than the cis-isomer and the (+)-form of the trans-isomer was more active than the (--)-form. Given by s.c. route, the (+)-transisomer E 382 was 1/3 as active as morphine. However, the Straub-tail reaction and the withdrawal jumping tests yielded more favourable results with L 201 and tramadol than with E 382.