Observational coding systems are uniquely suited for investigating interactional processes in couples and families, but their validity in diverse populations is unknown. We addressed this issue by applying factor analysis to interactional data collected from couples in low-income neighborhoods and coded with the widely used Iowa Family Interaction Rating Scales (IFIRS). Our sample of 414 low-income, ethnically diverse newlywed couples each provided 24-min samples of problem-solving and social support behavior. Interrater reliabilities were strong, and the resultant factors--reflecting positive, negative, and effective communication--were very similar to those obtained with White middle-class samples. Additionally, couples were more negative, less positive, and less effective in problem-solving conversations than in socially supportive conversations, further supporting the validity of the IFIRS in this population. We conclude by discussing the strengths and shortcomings of the IFIRS when used in a low-income, ethnically diverse population.