Low-loss planar and channel waveguides were fabricated in BK-7 substrates by ion exchange using dilute AgNO3/NaNO3 melts. waveguide refractive index profiles were inferred by comparison with effective refractive index measurements made on the guided modes. The diffusion constant of silver and its activation energy in BK-7 were calculated from the measured refractive index data. It was found that a post-exchange annealing of the waveguides resulted in a significant decrease in the waveguide losses. A Fabry-Perot waveguide resonator loss measurement technique was developed to measure the attenuation in these waveguides because of the unreliability of prism coupling methods at low-loss levels. Losses as low as 0.068 dB/cm were measured in channel waveguides.