40 subjects, 20 obese and 20 normal, were run on a weight-discrimination task requiring judgments dependent on proprioceptive feedback. A signal-detection analysis was used to separate sensory factors from non-sensory, response-bias factors in the analysis of the discriminations. Obese subjects were inferior to normals in ability to make sensory discriminations; the largest differences occurred between obese and normal males. Obese subjects also adopted a more strict criterion (beta); the largest differences again occurred for male subjects. Obese subjects showed more variability in their sensory judgments, although there was a significant difference on only one of the 5 discrimination tasks. Results are discussed in terms of the internal-external explanation of obesity.