When I was asked by the late Professor Wolfgang Bargmann in 1973 to write the continuation of his review article on the epiphysis cerebri published in the present Handbuch Series in 1943 I felt greatly flattered and readily agreed, not knowing that it is virtually impossible for a single person to cover comprehensively the vast field of pineal research carried out over the last 35 years. Although I have done my best to include as much of the relevant work as possible (up to July 1979), I am constantly haunted by the references I have missed. I sincerely apologize for these omissions: first, to the authors of these papers, who, in addition to working on one of the most stony grounds of biological research, now may experience the additional frustration of not being quoted; secondly, to my fellow pinealogists or pinealogists-to-be, who may carry out painstaking experiments only to find that they have been done before, or who may be led astray because of lack of information. Nevertheless, I do hope that this monograph will fulfil its aim, namely to show how pineal research has progressed over the last 35 years and where it stands today. It is hoped that it will aid in planning relevant experiments and that it shows which approaches to the pineal problem would be better avoided.