Four-fermion final states q (q) over bare(+)e(-) and q (q) over bar mu(+)mu(-) from neutral-current interactions in e(+)e(-) collisions are studied in the OPAL detector at LEP at centre-of-mass energies from 183 GeV to 209 GeV. The data analysed correspond to a total integrated luminosity of about 650 pb(-1) recorded from 1997 to 2000. Corresponding to the acceptance of the OPAL detector, a signal definition is applied requiring both leptons to have a scattering angle satisfying /costheta/ <0.95. Further requirements are made on the invariant masses of the fermion pairs. The extracted cross-sections for the processes e(+)e(-) --> q (q) over bare(+)e(-) and e(+)e(-) --> q (q) over bar mu(+)mu(-) are consistent with the expectations from the Standard Model. (C) 2002 Elsevier Science B.V. All rights reserved.