[en] Nernst coefficient measurements of La_0.88MnO₃ (T_c∼265 K) and La_0.7Ca_0.3MnO₃ (T_c∼265 K) are reported as a function of temperature (100-320 K) in moderate applied magnetic fields (0.38< H<1.8 T). For T>T_c, our data can be accounted for by the transport behaviour of small polarons. We find the semiconductor-metal transition is dominated by an increase in the hole density. For T≤T_c, an anomalous suppression of the Nernst coefficient was observed when the field increased from 0.38 to 1.8 T. The colossal magnetoresistance effect is attributed to a field-induced increase in the mobility of the charge carriers