Sexually mature female hake Merluccius merluccius with hydrated ovaries were sampled on a monthly basis in the Bay of Biscay, from May 1996 to October 1997 and from March to April 1998. The batch fecundity was positively related to total length. The relative batch fecundity (FBrel) varied significantly among months and years, but not between areas, i.e. International Council for the Exploration of the Sea Divisions VIIIa and VIIIb within the Bay of Biscay. Two levels of FBrel were found in 1997: the highest between January and April (mean ±s.e. 167 ± 5 eggs g−1) and the lowest from May to October (112 ± 3 eggs g−1). Population condition factor and gonado-somatic indices (IG) followed the expected trend in relation to the monthly changes in FBrel during 1997. The FBrel variation between years was 9% for 1996–1997 and 28% for 1997–1998, and the difference of the IG was c. 14 and 36%, respectively. Population relative egg production varied from a high value in January to March (985 eggs g−1) to a low egg production between April and October 1997 (445 eggs g−1).