Field trials were carried out using experimental CEEFAX data transmissions at the two information rates of 4.5 and 6.875 MBits/s. The purpose of the trials was to investigate the coverage or service area of CEEFAX in comparison to that of the associated colour television signal and to see if there were any special problems with the transmission and reception of CEEFAX which did not arise with colour television. The results indicated that CEEFAX was a rugged transmission system and that in general the size of the service area for CEEFAX transmission was greater than that for colour television. There was very little difference in the sizes of the service area for either the low or high data bit-rates.