Sunyaev-Zeldovich effect-derived distances to the high-redshift clusters MS 0451.6-0305 and Cl 0016+16

We determine the distances to the z similar or equal to 0.55 galaxy cluster s MS 0451.6-0305 and Cl 0016+16 from a maximum-likelihood joint fit to inte rferometric Sunyaev-Zeldovich effect (SZE) and X-ray observations. We model the intracluster medium (ICM) using a spherical isothermal beta model. We quantify the statistical and systematic uncertainties inherent to these dir ect distance measurements, and we determine constraints on the Hubble param eter for three different cosmologies. For an Omega(M) = 0.3, Omega(A) = 0.7 cosmology, these distances imply a Hubble constant of 63(-9-21)(+12+21) km s(-1) Mpc(-1), where the uncertainties correspond to statistical followed by systematic at 68% confidence. The best-fit H-0 is 57 km s(-1) Mgc(-1) fo r an open (Omega(M) = 0.3) universe and 52 km s(-1) Mpc(-1) for a flat (Ome ga(M) = 1) universe.