Monitoring the psychological and physiological activity of persons interacting with virtual humans poses exacting measurement challenges. Three experiments are reported in this paper. In these experiments we made use of Virtual Human Agent technology to assess persons' psychological and physiological responses to Virtual Standardized Patients. The first experiment provided support for the usability of the Virtual Standardized Patients through the use of a virtual character emulating an adolescent male with conduct disorder. In the second experiment we further developed the technology and aimed at assessing whether novice mental health clinicians could conduct an interview with a virtual character that emulates an adolescent female who has recently been physically traumatized. The third experiment looked at the usability of Virtual Standardized Patients for eliciting psychophysiological responses following exposure to virtual humans representing different ethnicities.