Pitfall trapping, dissections and laboratory rearing of Pterostichus madidus (F.) between I967 and I972 in north east England showed that the annual activity pattern of the species consists of four sections: (i) early summer activity of over-wintered, mostly female beetles; (ii) mid summer activity of newly emerged beetles of both sexes; (iii) late summer activity of maturing, mostly male beetles; (iv) autumn activity of mature and spent, mainly female beetles. Eggs were laid from August until November, with a peak at the end of August. The highest individual fecundity was 80 eggs, but many females laid few or no eggs, partly because of parasitism by Mermis nigrescens Dujardin (Nematoda). Fecundity was normally distributed among females laying ten or more eggs: the mean annual fecundity of these females varied from 20 to 44 eggs per female. Most females died in the autumn, but about a quarter of the female population probably survive the winter, and mature again in the following summer. Larvae developed throughout the winter, reaching the third instar by the spring: this stage has a partial diapause, which delays development at constant temperatures.