  The spectra of the planetary nebulae NGC3242 and NGC6369 are reanalysed using
spectral measurements made in the mid-infrared with the Spitzer Space Telescope
and the Infrared Space Observatory (ISO). The aim is to determine the chemical
composition of these objects. We also make use of International Ultraviolet
Explorer (IUE) and ground based spectra. These elliptical PNe are interesting
because they are well-studied, nearby, bright objects and therefore allow a
reasonably complete comparison of this type of nebulae. Abundances determined
from the mid-infrared lines, which are insensitive to electron temperature, are
used as the basis for the determination of the composition, which are found to
differ somewhat from earlier results. The abundances found, especially the low
value of helium and oxygen, indicate that the central star was originally of
rather low mass. The abundance of phosphorus has been determined for the first
time in NGC3242. The electron temperature in both of these nebulae is roughly
constant unlike NGC6302 and NGC2392 where a strong temperature gradient is
found. The temperature of the central star is discussed for both nebulae.
Finally a comparison of the element abundances in these nebulae with the solar
abundance is made. The low abundance of Fe and P is noted and it is suggested
that these elements are an important constituent of the nebular dust.
