Intra-individual variability in psychophysiological parameters of activation processes can be attributed to functional fluctuation and/or error of measurement. A repeated measurement design at intervals of about three weeks, three months and one-year duration, in which a laboratory-field comparison was made with respect to predictability of individual differences, provided data on a broad spectrum of physiological and psychological variables measured under various conditions. We investigated the reproducibility of commonly used laboratory measures in a sample of male students of physical education (N = 58). Results indicate that a hypothetical general trend component accounts for less than 10 percent of the total variance in a two-factorial ANOVA (Subjects X Replications). Stability coefficients based on raw scores (rest and strain scores) are relatively higher than those based on change scores. Stability of heart rate, pulse wave velocity, respiration rate during rest, mental arithmetic and cold pressor test and cardiovascular and respiratory parameters during ergometer exercise and 1000m run exceed the stability of blood pressure, parameters from impedance cardiography, eye blink and electrodermal activity during the respective laboratory conditions. The implications of such descriptive studies for the planning and evaluation of longitudinal studies and for selection of parameters depicting habitual dispositions in differential psychophysiological research are indicated.