A study was conducted to test the reliability and validity of the Intimate Coding System (INCS)--an instrument designed to code verbal conversation in intimate relationships. Subjects, 34 married couples, completed Spanier's Dyadic Adjustment Scale, which elicited information about relational adjustment and satisfaction in intimate couples in terms of four communication components: degree of consensus, cohesion, affectional express, and harmony in the relationship. After completing the scale, each couple then discussed two marital topics in a videotaped session. The first topic was based on expressed perceptual disagreements drawn from the Spanier scale and the second was based on J. M. Gottman's improvised marital conflict scenes. Two trained raters used the INCS to code all interactions as integrative, descriptive, or disintegrative behavior. After this coding had been completed, 10% of the interactions were recoded by the same raters. Results indicated that the intercoder and across-time reliability scores were high and satisfactory. Construct validity of the instrument was demonstrated through the statistically significant relationships between the three classes of INCS-coded behaviors with the conceptually related external variable, marital satisfaction. (FL)