Correlations between environmental measures and infant development have been shown to involve genetic as well as environmental components, as indicated by environment‐development correlations in non‐adoptive families that are greater than correlations in adoptive families. The goal of the present analysis was to search for aspects of parental behaviour that underlie genetic mediation of environment‐development relationships. Analyses focused on Bayley MDI scores at 2 years of age as a measure of developmental outcome, and the HOME as an environmental measure in a study of 233 adoptive families and 227 matched non‐adoptive families. Surprisingly, the results indicated that partialling out parental SES, education, IQ, specific cognitive abilities, and major dimensions of personality had little effect on the HOME‐Bayley relationship in either non‐adoptive or adoptive families. From these analyses we conclude that the parental factor which genetically mediates this relationship must be a genetically influenced factor which is not related to these traditional measures. Criteria are offered to guide the search for parental factors that can explain genetic mediation of the HOME‐Bayley