Several interesting hadronic states H are believed to be quasi-bound states of two
hadrons. Typical examples are : baryonium and Λ(1405). These are localized
below thresholds of these two hadrons and an experimental access is difficult.
Frequently it is also complicated by many decay channels. To reach below threshold
one needs bound nucleons, that is few nucleon systems, or final state interactions.
These usually allow to study H in inelastic processes but the description is technically
involved . Extraction of elastic amplitude related to H is more difficult.
I will try to present briefly some possibilities and, next concentrate on few results from