  The LaIn3-xSnx alloy system is composed of superconducting Pauli paramagnets.
For LaIn3 the superconducting critical temperature T_c is approximately 0.7 K
and it shows an oscillatory dependence as a function of Sn substitution,
presenting its highest value T_c ~ 6.4 K for the LaSn3 end member. The
superconducting state of these materials was characterized as being of the
conventional type. We report our results for Gd3+ electron spin resonance (ESR)
measurements in the LaIn3-xSnx compounds as a function of x. We show that the
effective exchange interaction parameter J_fs between the Gd3+ 4f local moment
and the s-like conduction electrons is almost unchanged by Sn substitution and
observe microscopically that LaSn3 is a conventional superconductor.
