In this proposal, more time is being requested for RRUBIN.IRON. We also propose observations that extend RRUBIN.IRON to a region of the Orion Nebula where we have obtained HST observations and which is NOT covered by reserved ISO targets. The iron abundance is of fundamental interest in astrophysics. Surprisingly little information about Fe abundances is available from gaseous nebulae, although progress has been made for Orion. HII regions provide a probe of the current mix of elements from which new stars are born. The most abundant Fe ionic species in HII regions are Fe++ and Fe+3. Much improved atomic data for Fe++ and Fe+3 ions have recently become available as part of the IRON atomic data project. We now include a 17-level atom treatment for Fe++ and a 12-level atom for Fe+3 in our photoionization codes to predict important line fluxes, including IR lines. Because there are many observable FeIII lines, there is an expanded opportunity to obtain reliable physical parameters - density, temperature, extinction, and the elemental abundance - that is not presented by other heavy element ions, where the collisionally excited lines arise from the lowest 5 or 6 levels only. We plan cospatial ISO and ground-based observa- tions. Even though Fe+3 is likely the MOST abundant Fe species in Orion, it does not have intrinsically bright lines under nebular conditions. Recently, we reported the first detection of an [FeIV] line in HII regions from our HST/GHRS observations of the Orion Nebula. From the expected relative strengths based on atomic data and our observations and model of Orion, the next most promising [FeIV] lines after those we observed with HST are the set of 6 NIR lines at 2.72-2.86 um. These lines are measurable only with ISO. We propose to measure the NIR FeIII and FeIV lines in Orion, which extends our priority 1 RRUBIN.IRON program where we observed the bright PN NGC 7009. We will test for an Fe depletion gradient in Orion. With merging of SW/LW lines, we can observe other important plasma diagnostic lines for very little extra time. Among these are [NeIII] 15.5 & [ArIII] 21.8 um, which will permit new density determinations for Orion.