Recent investigations have demonstrated greater variance in change in intellectual performance between different generations or age groups than is true for generalized developmental change across chronological age. Such findings have led to a careful investigation of certain environmental factors which might account for such change. A new instrument, the Life Complexity Inventory (LCI), was developed to measure both current and retrospective characteristics of the individual's life style and microenvironment. The LCI was completed by 140 individuals ranging in age from 40 to 88, whose intellectual and personality functioning had been measured in 1956, 1963, and 1970. Initial analysis of this instrument resulted in eight distinct environmental item clusters, which represent particular patterns of life style or experiences, family relationship, or relationship to the environment. Moderate correlations were found between environmental cluster scores and change in cognitive function over two consecutive seven-year periods. These changes in cognitive function were measured by The Primary Mental Abilities Test and the Test of Behavioral Rigidity. The grouping of individuals according to these eight item clusters resulted in the identification of four modal subject types; these types differ in their pattern of change in cognitive function over time. (Author/MV)