The daily data of the polarity of the interplanetary magnetic field for the years 1926--1982 were studied by means of a power spectrum analysis in order to determine prevailing structures of this polarity as well as to search for recurrences in those structures. On a global scale, the presence of significant peaks at about 27.5, 13.5, 9.1 and 6.8 days was observed, with amplitudes decreasing in that same order. However, for shorter intervals of time (of the order of 1 year) the resulting spectral distribution does not necessarily present the same characteristics, particularly concerning the relative power of the peaks at about 27.5 and 13.5 days. These results are interpreted,through a simulation with rectangular waves, as cases that correspond either to a two-sector or to a four-sector structure, when the dominant peak is that of about 27.5 or 13.5 days, respectively. Thus, by performing an annual survey of the data, it was found that there is a continuous change in the type of dominant structure, with intervals having a well-defined two-sector structure alternating with those having either a less defined structure or a well-defined four-sector structure. A further application of the power spectrum technique to this type of alternating variability in the dominant structures led to the conclusion that significant periodicities of about 3.7 and 1.5 years seem to exist in such a variability. These periodicities become important when compared to similar ones reported in studies of solar and geomagnetic activity. Other less significant periodicities in this alternated variability are also reported and discussed. Finally, a study of variations in the period corresponding to the peak of about 27.5 days was also accomplished, showing that it changes from about 28 days at the beginning of the solar cycle to about 27 days at the end of the cycle, as also found by other authors. ¿American Geophysical Union 1987