This study concerns oil-in-water microemulsions stabilized by a nonionic surfactant plus a few mole percent of an ionic surfactant at low droplet volume fraction (phi < 0.15). The interactions in these weakly charged systems have been studied by using turbidity measurements. In the absence of added ionic surfactant, the microemulsion droplets behave as hard spheres at low temperatures close to the lower temperature phase boundary. Increasing the temperature causes the turbidity to increase due to either droplet growth, clustering of droplets, or a combination of both effects. Droplets with added ionic surfactant show a decreased turbidity due to electrostatic repulsion between the droplets. The turbidity of charged droplets is temperature independent up to the upper temperature phase boundary of the single-phase microemulsion region. Increasing the temperature above the upper temperature phase boundary causes a sharp increase in turbidity. At the low temperature phase boundary, the variation of microemulsion turbidity with concentration of ionic surfactant (either anionic or cationic), droplet radius, and concentration of added electrolyte is semiquantitatively predicted by a simple theory with no adjustable parameters.