New theoretical electron-density-sensitive FexII emission line ratios Rl = 1(3s23p s 4S3 2 -3s3p 4 4Ps.2)/l(3s23p3 2p3.2 -3s3p 4 205.,2) and R2 = l(3s23p 3 2p32 -3s3p 4 2D~,2)/I(3s23p3 4S3 2 -3sZ3p 3 2P3,z) are derived using R-matrix electron impact excitation rate calculations. We have identified the FexJl 3s23p 3 4S3 2 -3s3p 4 4p5:2, 3s23p s 2p3.2 -3s3p 4 ZDs,z, 3sZ3p 3 4S3.2 -3s23p 3 2P3.2 and 3s23p 3 4S3. a -_ 3s23p3 2pj '2 transitions in an active region spectrum obtained with the Harvard S-055 spectrometer on board Sk)'lab at wavelengths of 364.0, 382.8, 1241.7, and 1349.4 ~,, respectively. Electron densities determined from the observed values of R~ (logN e _~ 11.0) and R a (logN~-~ 11.4) are significantly larger than the typical active region measurements, but are similar to those derived from some active region spectra observed with the Slcylab 2082A instrument, which provides observational support for the atomic data adopted in the line ratio calculations, and also for the identification of the Fe xlI transitions in the S-055 spectrum. However the observed value of R 3 = I( 1349.4 .,~)/I(1241.7 .~) is approximately a factor of two larger than one would expect from theory which, considering that the 1349.4 A. line lies at the edge of the S-055 wavelength coverage, may reflect errors in the instrument efficiency curve. Another possibility is that the 1349.4 .~ transition is blended, probably with Sin 1350.1 A..