This paper derives upper bounds on the masses of supersymmetric particles, specifically charginos, neutralinos, gluinos, and squarks, based on the "naturalness" criterion. The authors, R. Barbieri and G.F. Giudice, use low-energy supergravity models to analyze the electroweak symmetry breaking scale, $M_Z$, as a function of the top quark mass, $m_t$. They impose a naturalness condition that limits the fine-tuning of parameters to within one order of magnitude, leading to upper bounds on the masses of these particles. These bounds are derived for different values of $m_t$ and are shown to strongly differentiate between weakly interacting particles (charginos and neutralinos) and strongly interacting particles (gluinos and squarks). The results suggest that $e^+e^-$ colliders could be the most efficient machines for discovering supersymmetry if no supersymmetric particles are found below these limits. The paper also discusses the implications of these bounds for testing or disproving low-energy supersymmetry.This paper derives upper bounds on the masses of supersymmetric particles, specifically charginos, neutralinos, gluinos, and squarks, based on the "naturalness" criterion. The authors, R. Barbieri and G.F. Giudice, use low-energy supergravity models to analyze the electroweak symmetry breaking scale, $M_Z$, as a function of the top quark mass, $m_t$. They impose a naturalness condition that limits the fine-tuning of parameters to within one order of magnitude, leading to upper bounds on the masses of these particles. These bounds are derived for different values of $m_t$ and are shown to strongly differentiate between weakly interacting particles (charginos and neutralinos) and strongly interacting particles (gluinos and squarks). The results suggest that $e^+e^-$ colliders could be the most efficient machines for discovering supersymmetry if no supersymmetric particles are found below these limits. The paper also discusses the implications of these bounds for testing or disproving low-energy supersymmetry.