The Theta-z relation for HST bulges and disks out to Z approximately equal 0.8

We present HST scale lengths and ground-based redshifts for 63 faint field galaxies down to I <~ 21.5 mag from the Medium-Deep Survey. These have measured redshifts z <~ 0.8 and half-light radii 0.1" < r_e_, r_s_ < 5". We present the {THETA}-z relation for r^1/4^-bulges and exponential disks separately for world models with q_0_ = 0.0-1.0. We show that selection against low surface brightness galaxies in the HST images and ground-based spectra is comparable to that in local surveys. We compare our HST disk-dominated galaxies to a magnitude-limited subsample of the ESO-Uppsala local spirals. Extrapolating the best-fit local exponential disk scale length (r_s_ = 3.5 kpc for H_0_ = 75) out to z = 0.8, we find a rather symmetrical distribution of HST disks around this value. This implies that galaxy disks have been stable since z~0.8. We compare our HST bulge-dominated galaxies with r^1/4^ profiles to a magnitude-limited subsample of local Seven Samurai ellipticals. The latter have a local best fit r_e_ = 5.7 kpc. Our HST bulge sample shows a similar distribution for z <~ 0.8. Elliptical galaxy scale lengths have thus also remained rather constant since z <~ 0.8. We set limits to their possible evolution.