We aimed to compare plotting accuracy and interpretation of weight gain patterns in average and small infants on road-to-health (RTH) and the new World Health Organization (WHO) growth charts in Enugu, Nigeria. Child health staff plotted standard weights on both formats. Twelve plotted charts were created, permutating three different weight trajectories (fast, steady, and slow) ending at two attained weights (average and small), with each plotted on both chart formats. Respondents were shown four of these charts and asked to describe the weight gain pattern shown and what action this pattern would prompt. There were 222 respondents, of whom 78% were hospital based; 54% were nurses, 32% medical doctors, and 13% nutritionists. Plotting accuracy was good on both the WHO and RTH charts, but rating of weight gain was generally poor. On the RTH chart, slow weight gain was correctly recognized in only 19% average and 35% small infants, and responses were not significantly associated with the pattern shown. On the WHO charts, slow weight gain was correctly recognized in 40% average and 65% small infants ( p = .002 and <.001), but they were also more likely to rate small children with normal growth as slow weight gain. In a logistic regression model, final weight predicted a slow weight gain rating more strongly (OR = 2.4; 1.8-3.2) than an actual slow weight gain pattern (OR 1.8; 1.1-1.6). Health staff seemed unable to recognize slow weight gain and were influenced more by current weight than actual weight gain pattern, though the new WHO format improved recognition. [ABSTRACT FROM AUTHOR]