Morphological evaluation of embryos is essential to the success of emb
ryo transfer procedures and is presumed to reflect embryo metabolic ac
tivity. To investigate this assumption, correlations between morpholog
ical and metabolic parameters were determined for cultured murine moru
lae. After 18 h (n = 47) or 36 h (n = 48) of culture in M16, the devel
opmental rate and quality (poor or good) of embryos were estimated, an
d, then, either their C-14-glucose utilization or S-35-methionine upta
ke and incorporation were measured. Retarded developing, or poor-quali
ty embryos had lower mean glucose utilization, uptake and incorporatio
n rates than normally developing or good-quality embryos (P < 0.05) Af
ter 18 h of culture, an association was found between developmental ra
te and metabolic activity, but this was not evident after 36 h of cult
ure. Similarly, an association was found between embryo quality and me
tabolic activity. As expected, poor embryo quality was indicative of l
ow metabolism throughout the culture period, but good quality did not
necessarily indicate normal metabolic activity. Thus, morphological pa
rameters do not always reflect metabolic competence, and some function
al defects were not detectable by visual evaluation alone. Measuring m
etabolic parameters could complement visual evaluation for a better se
lection of embryos prior to transfer.