Several experiments were conducted with starved and fed females of the arctic copepod Calanus hyperboreus to investigate 1) their life span, reproductive period, egg production and egg viability ; 2) to study the effect of origin, ie Atlantic and Arctic waters in the Greenland Sea, on the timing of reproduction; and 3) to study the effect of time of collection on the onset of reproductive activity as a first approach to study control mechanisms of the reproductive cycle. Females collected in October produced up to 1000 eggs and had a maximum life span of 164 days without feeding, whereas fed females produced up to ca. 6000 eggs and survived up to 806 days. These observations support earlier assumptions that females were multiannual-iteroparous, ie capable to spawn in successive years, which would be unique for calanoid copepods. In starved females clutch size decreased significantly with each spawning event. Viable eggs were produced during most of the life time. There was no difference in the timing of reproductive activitiy between females from the Westspitsbergen Current and the Greenland Sea Gyre. Fed and starved females collected in May and June began to spawn circa two and four months after collection, respectively, whereas females collected in August and October started spawning at the same time, in the middle of October. This indicates initiation of reproductive activity in the field in August, coincident with the descent into deep waters. Potential cues for the untimely spawning of females collected in spring, and "unnatural" feeding in fall experiments are discussed. Their large size, robustness and combination of different types of diapause in their life cycle makes C. hyperboreus a good model organism to study diapause control mechanisms.