Confirmatory analysis was used;to specify behavioral domains from resu
lts of the Assessment for Preterm Infants' Behavior (APIB). The APIB m
easures both task performance and quality of performance, which theore
tically improves the possibility of discriminating infant functional c
apacity beyond that obtained by measuring task performance exclusively
. We hypothesized that the APIB measures six behavioral domains, inclu
ding overall modulation of behavior, availability for examination, mot
or competency, sociability, habituation, and reactivity. The subjects
were a medically heterogeneous group of 145 infants who required neona
tal intensive care. Data from 157 behavioral and 41 reflex items, out
of a possible 280 items, were used. The model was highly acceptable by
several practical indices of fit (Bentler-Bonett Normed Fit Index = .
994; Bentler-Bonett Nonnormed Fit Index = .999; Comparative Fit Index
= .999). The six behavioral constructs are clinically understandable a
nd parsimonious with respect to the behavioral measures included. The
results suggest that prerequisites for social interaction of infants r
equiring neonatal intensive care include both overall modulation and a
vailability, which are unique and distinct from each other and from mo
tor competency and habituation.