Describes a model of developmental potential that defines 5 parallel dimensions or modes of mental functioning assumed to be genetically independent of one another. The 5 modes encompassed by the model are represented by 5 forms of “psychic overexcitability.” The prefix over in overexcitability is meant to convey that this is a special kind of responding, experiencing, and acting that is enhanced and distinguished by characteristic forms of expression. The 5 forms are psychomotor overexcitability (P), intellectual (T), emotional (E), and imaginational (M). The model was tested in a study with 49 gifted adolescents (aged 12–17 yrs), 28 gifted adults (aged 22–55 yrs), 19 artists (aged 18–59 yrs), and 42 graduate students (aged 22–50 yrs). Results of assessment on an overexcitability questionnaire indicate that both gifted adolescents and gifted adults were characterized by 2 nonintellectual factors—M and E–and by T overexcitability. It is concluded that while the level of each overexcitability variable differs considerably across gifted individuals, they are consistently and reliably present in a gifted group of any age.