Preliminary analysis of Mariner II magnetometer data indicates a persistent interplanetary field varying between a least 2 and 10 gamma (1γ = 10 -5 gauss). The interplanetary field appears to lie mainly in the ecliptic plane, although there is a substantial, fluctuating, transverse component. The Mariner II data agree reasonably well with the prior Pioneer V observations. Typically, variations as large as 5 to 10 gamma in the field component radial from the sun are measured. Correlations with the Mariner II plasma measurements have been observed.