  The Chaplygin gas (CG) and the generalized Chaplygin gas (GCG) models,
proposed as candidates of the unified dark matter-dark energy (UDME), are
tested with the look-back time (LT) redshift data. We find that the LT data
only give a very weak constraint on the model parameter. However, by combing
the LT with the baryonic acoustic oscillation peak, we obtain, at the 95.4%
confidence level, $0.68\leq A_c\leq0.82$ and $0.59\leq h\leq0.65$ for the CG
model, and $0.67\leq A_s\leq0.89$ and $-0.29\leq \alpha\leq0.61$ for the GCG
model. This shows that both the CG and the GCG are viable as a candidate of
UDME. Within the GCG model, we also find that the Chaplygin gas model
($\alpha=1$) is ruled out by these data at the 99.7% confidence level.
