Loss of eggs during the incubation period in ovigerous females of Nephrops norvegicus from the Bay of Biscay is calculated using two different methods. The first calculates the egg loss from incubation stage A to stage D. The second calculates the loss between the end of ovary maturation and incubation stage D. The first method may contain a bias which decreases the loss estimation : loss of eggs during trawling may be higher in stage A than in stage D. In the Bay of Biscay, the loss of eggs in ovigerous females of Nephrops norvegicus would be about 45-50% for the entire incubation period. Our result is quite different from the 75% obtained by other workers in Portuguese waters. Loss of eggs during incubation which may be due mainly to predation may be a means of density regulation (stock-recruitment relationship). The differences observed in loss of eggs between the South-Brittany area and Portuguese waters may result from differences in fishing mortalities or in the density of predators. [NOT CONTROLLED OCR]