We investigated the activity pattern of males and females of the neotropical harvestman Neosadocus maximus Giltay 1928 focusing on behavioral variations between day and night and also between summer and winter. Our study also proposes a new method for quantifying arthropod behavior in captivity based on totally random samplings, which minimizes problems of pseudoreplication, so common in studies of behavioral repertoires. Eighteen individuals (nine males and nine females) collected at the Parque Estadual Intervales, São Paulo state, Brazil, were maintained in the laboratory from June 2003 to February 2004 for qualitative and quantitative observations. Thirty-four behavioral acts grouped in five behavioral categories were recorded, with “resting” (53.1%) and “exploration” (30.8%) being the most frequent. The behavioral repertoire of males (32 acts) was more diversified than that of females (29 acts). Moreover, there was a significant effect of sex (male × female) on the frequency of the behavioral categories: females expended more time resting than did males, whereas males expended more time in exploration and grooming activities than did females. There was also a significant effect of time of day (day × night) and of season (winter × summer) on the frequency of the behavioral categories: individuals were most active at night and during summer. Finally, temperature, but not humidity, had a positive effect on the activity of the individuals. In conclusion, the activity of N. maximus has sexual, daily, and seasonal variations, which are both quantitative and qualitative.