Pillow lava samples dredged from the rift valley of the Mid-Atlantic Ridge (FAMOUS area) are oriented according to their cooling position on the seafloor (paleovertical) by the segregation vesicle technique (Bideau et al., 1977). Assuming that the spatial distribution of the oriented vesicles corresponds to a Fisherian distribution,, it is possible to compute the dispersion coefficient K from the characteristics of the planar distributions (Von Mises distributions). From a theoretical point of a view a high probability of finding crescent-shapedd segregation vesicles in thin sections of ocean floor basalts is suggested, and the distribution of the oriented crescents should have huigher precision parameter k in sections approaching the paleovertical. However, from a srt of 100 roccks, only 27 samples exhibit enough segregation vesicles to provide meaningful directional averages. The paleovertical inicated by segregation vesiclles is usually poorly definned in spite of the large nummber (commonly, ~100) of angular determinations for each rock. The mean preccision parameter K is low (~3), the λ 95% confidence semi-angles are large (typically, 15¿). Moreover, the calculated magnetic inclinations are almost randomly distributed, which suggests that either the preferential orientation of the segregation vesicles does nnot correspond to the paleovertical or that the rocks rotate betwen the temperature of segregation (>1000¿C) and the temperature of magnetization (<300¿C), generally). Within onne of our pillows the occurrence of rotations at high temperature is