To delineate quantitatively differences in suck-swallow-respiration coordination during feeding in term infants exposed to drugs in utero, 16 control infants (10 females, six males; mean birthweight 3209g, standard error of the mean [SEM] 103g) and 15 drug-exposed infants (seven females, eight males; seven cocaine, eight opiates; neonatal abstinence [Finnegan] scores less than 10; mean birthweight 3001g, SEM 93g) were studied in the first three days of life and again at one month of age. Coefficients of variation (COVs) of suck-suck, swallow-swallow, and breath-breath intervals were used as measures of stability of individual rhythms. COVs of suck-swallow and swallow-breath intervals were used to determine stability of multiply integrated rhythms. In the first three days of life, a significantly higher percentage of 'apneic swallows' (runs of three or more swallows not associated with breathing movements, divided by total run-swallows) was noted during feeding in the drug-exposed infants (mean 5.3% SEM 1.7%) compared with controls (mean 0.9%, SEM 0.4%;p<0.02), who also had less breath-breath rhythmic stability (higher COV) and shorter swallow-breath intervals. These differences were no longer evident at one month of age. Opiate-exposed infants were generally more affected than the cocaine-exposed infants. Swallowing was less rhythmic in the drug-exposed cohort, especially in opiate-exposed infants, but this difference also disappeared by one month. In the first days of life, drug-exposed infants were less efficient feeders, ingesting less volume per run-swallow than controls (mean 0.31ml, SEM 0.05ml, versus 0.45ml, SEM 0.05ml;p<0.05). The decreased efficiency appeared to be compensated for by a slightly faster swallow rate (mean 53 swallows per minute SEM 2 versus 47 swallows per min, SEM 1, in controls;p<0.005). By one month of age these differences between groups had disappeared as well. Intrauterine drug exposure, even in infants with relatively mild symptoms of withdrawal, may adversely impact development of brainstem respiratory and swallow centers, thus affecting, albeit transiently, the underlying biorhythms of feeding.