A dielectric plunger displaces liquid filling a short section of coaxial line, and dielectric constant and loss are determined from changes in measured capacitance and conductance with displacement. Corrections for imperfect plunger fit, lead capacitance, and inductance are small and well defined, and procedures for making them are given. Dielectric constants from 3 to 300 and high losses can be measured from −70 to 100°C with 3 cc or less of sample.