The Kuiper Airborne Observatory has been used to make measurements of the infrared forbidden lines of (SIII) 18.72μm, (NeV) 24.28μm and (OIV) 25.87μm in eight planetary nebulae. In all cases the beam was larger than the emitting region. The observed line fluxes are used to determine ionic abundances under the assumption of constant density throughout the relevant volume as determined by optical observations. In some cases the NeV near UV lines are used in conjunction with the infrared measurements to determine the electron temperature in the NeV emission regions. The (SIII) 33.47μm line can be used with the (SIII) 18.72μm line flux to characterize the clumping within the nebulae.