  The scaling properties of self-avoiding tethered membranes at the tricritical
point (theta-point) are studied by perturbative renormalization group methods.
To treat the 3-body repulsive interaction (known to be relevant for polymers),
new analytical and numerical tools are developped and applied to 1-loop
calculations. These technics are a prerequisite to higher order calculations
for self-avoiding membranes. The cross-over between the 3-body interaction and
the modified 2-body interaction, attractive at long range, is studied through a
new double epsilon-expansion. It is shown that the latter interaction is
relevant for 2-dimensional membranes at the theta-point.
