We propose to map with ISOPHOT three low-background fields
 containing at least one COBE pixel (0.32 deg x 0.32 deg) in three
 wavelength bands (25 micron, 100 micron, 180 micron). With these
 measurements we want
 -- to detect arcminute structure in the zodiacal light and hence
    the interplanetary dust cloud
 -- to search for extragalactic background light in the cosmological
    window longward of 100 micron and for the brightness
    fluctuations associated with it
 -- to better relate the COBE and ISO calibrations for wavelenghts
    relevant to zodiacal light and extragalactic background light,
    in particular for the brightnesses of low-background fields.
 With this proposal we expand similar measurements, which were
 contained in the guaranteed time programme at a minimum level,
 to a more significant coverage.

	NOTE: These are no fixed time observations, but there are optimum
		dates for the observations to be performed. See table in the
		introductory part of the Jusitification	section.

	NOTE: These are no concatenated observations to keep a better chance for
		them to be scheduled, but they gain considerably scientifically
		if performed close in time (within one orbit or a few days).

  	NOTE: Absolute calibration is very important for these observations.
		Calibration of the used instrument modes therefore should be
		done as closely as possible before or after the measurements,
		optimum would be in the rpeceding or following orbit.