The reproductive cycle of the razor clam Solen marginatus (Pulteney 1799) was studied in three different locations of Spain. Sampling was performed in the natural beds of: Eo Estuary (NW Spain) in 1994 to 1995, Santander Bay (N Spain) in 1998 to 1999 and Terrón Estuary (SW Spain) in 1999. In Eo, Santander and Terrón, respectively: phase 0 (resting stage) occurred in July to August, September to October and August to September, phase I (proliferation of gonias) happened in: August to October, October to December and September to November, phase II (gametogenesis) was developed in November to April, January to May and December to April and phase III (reproduction) took place in: May to June, June to August and May to July. Two new approaches oriented to the fast monitoring of the gametogenic cycle of the species based on sequential mean drained soft parts weights obtained by simulation and on the macroscopic observation of the gonad are presented.