Early detection attenuates otherwise high mortality from the skin cancer melanoma, and although major melanoma symptoms are well defined, little is known about how individuals detect them. Previous research has focused on identifying static stimuli as symptomatic vs. asymptomatic, whereas under natural conditions it is "changes" in skin lesions that most demand vigilance. Three experiments explored detection-of-change behavior using a series of images in which melanoma symptoms gradually increased in severity. Goals included exploring perceptual properties of the images in generalization-testing and modified psychophysical procedures, and examining the smallest amount of change in symptom severity that was detected in laboratory conditions vs. an approximation of field conditions. Precise measurement of detection behavior is seen as a prerequisite to evaluating the effectiveness of interventions for improving skin self-examination. (Contains 4 figures, 2 tables and 2 footnotes.)