Polychaetes are important components of the intertidal sandflat community in Lawson’s Flat, Dillon Beach, California. Little is known about the factors that control the relative abundance of these species. In view of the extensive evidence of the importance of interactions between component species in intertidal communities it is of interest to obtain information that would facilitate future experimental work of such interactions. This study documents seasonal changes in the abundance of the polychaete component of the intertidal community. Attention is directed at possible factors that might affect seasonal changes in distribution. A major finding is that certain herbivorous polychaetes exhibit seasonal fluctuations in abundance that appear to be correlated with changes in algal cover. These findings might suggest more detailed future experimentation. Some aspects of recruitment of major species are considered and the presence of a parasite in one of the species is noted. Aspects of benthic community ecology are discussed.