HERBERT FISCHER Max-Planck-Institut fur Immunbiologie, Freiburg-Zahringen With 3 Figures Ladies and Gentlemen: On behalf of the organizers of the 22nd Mosbach Colloquium, Msrs. HOLZL-WALLACH, STOFFEL, WIEGANDT and myself, I bid you all a hearty welcome. We thank you all for coming and naturally feel particular appreciation for the presence of the invited speakers. But, thanks to the tradition that the Mosbach Colloquia have enjoyed for 22 years we did not need to work very hard, since most of our invitations were accepted without hesitation. Perhaps some of you will wonder why Mosbach and its tradi­ tion means so much, especially to the older ones amongst us. In any event, at a time when we were much hungrier and thirstier than we are today, Mosbach became a unique place where we could satisfy our spiritual as well as our physical hunger. It was here where we could find the friendly and peaceful atmosphere which helped us to establish contacts with colleagues from foreign coun­ tries and from distant scientific fields, which often led to lasting communication and cooperation. The initiator of these Colloquia, my teacher Kurt Felix, im­ parted to these gatherings a pioneer spirit which is more needed today than in the past, particularly because we are now 500 rather than 50 to 100 participants. Indeed, we as organizers, have had to ask ourselves whether it is still possible to have an exciting lecture series combined with the leisure and opportunity for spontaneous questioning and stimulating individual discussion.