This paper reviews the chronopsychological studies which analyse circa
dian rhythms and limit their measurements to the diurnal period of hea
lthy adult subjects. An introductory section includes a description of
the general concepts of rhythmicity, findings of the underlying biolo
gical mechanisms and the problems derived from the study of behavioral
rhythms. The various behavioural tasks are categorized according to t
he classification system proposed by the author (Adan, 1993b). Behavio
ral tasks are grouped into two main categories, subjective and objecti
ve. The later subclasified in turn as simple and complex tasks. Finall
y, the most outstanding results reported in psychological studies on r
hythms which show a smaller or greater periodicity than circadian, are
discussed.