The gas composition of the troposphere of Jupiter in the clearest regions of the North Equatorial Belt (NEB) was derived from the Voyager 1 IRIS data. The infrared spectrum for this homogeneous ''cloud-free'' region was modeled to infer altitude profiles for NH/sub 3/, PH/sub 3/, CH/sub 3/D, GeH/sub 4/, and H/sub 2/O. The profiles for NH/sub 3/ and PH/sub 3/ were found to be depleted in the upper troposphere but otherwise in agreement with their solar values at the 1 bar level. The mole fraction for CH/sub 3/D was determined to be 3.5/sup +1.0//sub -1.3/ x 10/sup -7/. The GeH/sub 4/ mole fraction of 7 +- 2 x 10/sup -10/ at the 2-5 bar level is a factor of 10 lower than the solar value. The H/sub 2/O mole fraction is approx.1 x 10/sup -6/ at the 2.5 bar level and is increasing to approx.3 x 10/sup -5/ at 4 bars where it is a factor of 30 lower than solar. Using IRIS inferred values for the mole fractions of CH/sub 3/D and CH/sub 4/ a value of D/H = 3.6/sup +1.0//sub -1.4/ x 10/sup -5/ is derived. Assuming this Jovian D/H ratio is representative of the protosolar nebula, andmore » correcting for chemical galactic evolution, yields a value of 5.5--9.0 x 10/sup -5/ for the primordial D/H ratio and an upper limit of 1.8--2.4 x 10/sup -31/ g cm/sup -3/ for the present-day baryon density.« less