Racemic or optically active 1‐(p‐hydroxybenzyl)‐1,2,3,4,5,6,‐7,8‐octahydroisoquinolines (I, Ia or Ib) as well as their O‐methyl‐ethers (II, IIa or IIb) are dehydrogenated in good yields to 5,6,7,8‐tetrahydroisoquinoline derivatives at higher temperature. The conversion of the latter into racemic 1‐(p‐hydroxybenzyl)‐1,2,3,4,5,6,‐7,8‐octahydroisoquinoline (I) or to the racemic O‐methyl ether (II) is achieved either by reduction with sodium in isoamyl alcohol or by catalytic reduction of the quaternary bromobenzylates by way of the tertiary N‐benzyl ‐1,2,3,4,5,6,7,8‐octahydroisoquinolines.