Neurobehavioural toxicity in occupational lead-exposure has typically not been observed at blood lead-concentrations (PbB) below 400 micrograms/l (e.g. 1, 2), whereas in environmentally exposed children such deficit has been reported to occur down to PbB of 100-150 micrograms/l and, perhaps, even below this range (4). Both cross-sectional and prospective studies have arrived at similar conclusions in this respect. The preferred endpoint in most such studies has been the IQ-measure, which has good psychometric qualities, is sufficiently well standardized to be comparable across studies, and exhibits attractive simplicity for the regulator in a public health context. Metaanalyses on both cross sectional and prospective studies in lead exposed children have concluded that a typical doubling of PbB from 100 to 200 micrograms/l is associated with an average loss of IQ of 1-3 points (3, 4). It should also be pointed out, however, that the IQ-focus has also interfered with systematic efforts to identify more specific lead-induced functional deficits by means of more detailed neurobehavioral analyses (5). Some neuropsychological findings in lead exposed children suggest that part of the impairment resembles performance deficit found to be characteristic for children presenting with signs and symptoms of attention deficit disorder.