The relation between two-flash thresholds (TFTs) and electrodermal activity—skin conductance level (SCL) and skin potential level (SPL), of paranoid and nonparanoid schizophrenics and normal controls was examined in activated and nonactivated conditions. A bicycle ergometer which induced significant changes in heart rate was used as an activator. At low levels of skin potential and skin conductance the two-flash thresholds of the controls were positively related to skin potential and skin conductance whereas at higher levels of skin potential and skin conductance, and in activated conditions, a negative relation was found. In general the two-flash thresholds of both schizophrenic groups were negatively related to skin potential and skin conductance in nonactivated conditions; when activated the paranoids showed the same changes as normals while the nonparanoids showed raised two-flash thresholds and lowered skin conductance levels. These findings are interpreted as showing the operation of inhibitory processes, consonant with the concept of protective inhibition, elicited as somatic arousal increases in nonparanoid but not paranoid schizophrenics.