Tests of CPT and Lorentz symmetry using neutral-meson oscillations are stud
ied within a formalism that allows for indirect CPT and T violation of arbi
trary size and is independent of phase conventions. The analysis is particu
larly appropriate for studies of CPT and T violation in oscillations of the
heavy neutral mesons D, B-d, and B-s The general Lorentz- and CPT-breaking
standard-model extension is used to derive an expression for the parameter
for CPT violation. It varies in a proscribed way with the magnitude and or
ientation of the meson momentum and consequently also with sidereal time. D
ecay probabilities are presented for both uncorrelated and correlated meson
s, and some implications for experiments are discussed.