Measurement of pain in pre-verbal infants is complex. Until now, pain behavior has mainly been assessed intermittently using observational tools. Therefore, we determined the feasibility of long-term, objective and continuous measurement of peripheral motor parameters through body-fixed sensors to discriminate between pain and no pain in hospitalized pre-verbal infants. Two pain modes were studied: for procedural pain 10 measurements were performed before, during and after routine heel latices in 9 infants (age range infants: 5-175 days), and for post-operative pain 14 infants (age range 45-400 days) were measured for prolonged periods (mean 7 h) using the validated COMFORT-behavior scale as reference method. Several peripheral motor parameters were studied: three body part activity parameters derived from acceleration sensors attached to one arm and both legs, and two muscle activity parameters derived from electromyographic (EMG) sensors attached to wrist flexor and extensor Muscles. Results showed that the accelerometry-based parameters legs activity and overall extremity activity (i.e. mean of arm and legs) were significantly higher during heel lance than before or after lance (p <= 0.001), whereas arm activity accelerometry data and Wrist Muscle activity EMG data showed no significant change. For the post-operative pain measurements, relationships were found between accelerometry-based overall extremity activity and COMFORT-behavior (r = 0.76, p < 0.001), and between EMG-based wrist flexor activity and COMFORT-behavior (r = 0.55, p < 0.001, for a subgroup of 7 infants). We Conclude that long-term, objective and continuous measurement of peripheral motor parameters is feasible, has high potential, and is promising to assess pain in pre-verbal hospitalized infants. (c) 2007 International association for the Study of Pain. Published by Elsevier B.V. All rights reserved.