Abstract: The relationship between IMF B_s. events (B_s > 10nT, VB_s > 5mV/m andboth last more than 3h) and intense magnetic storms (Dst≤ -100 nT) is analyzedusing the solar wind and geomagnetic data from 1978-1988. The results showthat one hundred percent of B_s events can cause magnetic storms, but only 84% areintense storms. Although all the intense magnetic storms correlate to larger IMF Bsclosely only 68% of intense magnetic storms are actually caused by B_s events. Therelationship between B_s events and intense magnetic storms is not in correspondenceof one to one. The effects of magnetospheric background and fluctuations of B_s onthe cause of magnetic storms must be taken into account. Also the attention shouldbe paid to the fact that Dst indices are affected by many electric current systemsafter than ring current.