3-FOLDS IN P(5) OF DEGREE-12

Let X be a 3-dimensional submanifold of P5 of degree 12. This article gives, up to one case, a complete classification of the deformation cl asses of those 3-folds. The main tools used are methods already applie d in the classification of degrees 9 to 11 and adjunction theoretic re sults. We show here how the 2nd reduction of X can be applied to analy ze the birational structure of X or even exclude the existence of X.