Tidal stresses beneath the oceans can be up to an order of magnitude higher than those found in the continents because of the eects of loading by ocean tides. I have analyzed 1899 microearthquakes recorded during a 55-day experiment on the Endeavour segment of the Juan de Fuca Ridge for tidal triggering. The tidal phase of the full data set and of a declustered subset comprising 987 events appears non-random to a high level of condence. Earthquakes occur more frequently near low tides, especially the lowest spring tides, when the extensional stresses are a maximum in all directions.