The photospheric filling factor of the active binary II Pegasi

U BV and JHK photometry of the active single-lined binary II Peg, we perfor med in 1995, is presented. A method to determine the fraction of the photosphere covered by spots (fil ling factor) and to check the accuracy of generally assumed: values of phot ospheric parameters has been developed. The procedure is based on the compa rison between multiband fluxes and low resolution synthetic spectra weighte d on the base of the spot filling factor and scaled with the ratio between the star radius and distance (R/d), so that we can also estimate the R/d ra tio. A chi(2) fit has been performed for II Peg observations close to the l ight maximum and minimum by assuming reliable values of the photospheric pa rameters. Although a unique solution cannot be reached, we found clear indi cation for a spot filling factor at light maximum greater than or equal to 40%. We find that the same set of parameters that gives us the best fit sol utions at light maximum also provides the best fit at light minimum. The re sulting solutions are consistent with the observed amplitude of the photome tric wave, and with the commonly accepted value of R, unspotted V magnitude and spectral classification for II Pegasi.