The present investigation compared the values obtained for the intestinal crypt cell production rate per hour (CCPR) at several sites in the intestine of rats using two variations in the application of metaphase arrest technique. The CCPR was determined both from the slope of a metaphase accumulation line obtained by linear regression analysis of measurements at several time points and by the single time point accumulation method. The comparison was performed for both the steady state in untreated controls and under perturbed conditions at 6, 12 and 24 h following intraperitoneal administration of 1000 mg/kg bodyweight of hydroxyurea to rats. In the steady state, the metaphase accumulation values were linear up to 3 h after vincristine sulfate in the proximal intestine (stomach to proximal ileum) and linear for up to 3 1/2 n in the distal ileum and the colon. Consequently the 3 h time point was selected for evaluation of CCPR values using the single time point method. The two methods gave equivalent results in the steady state, although in situations where there was good linearity of metaphase accumulation, the values obtained by the regression method were usually more precise. In the perturbed intestine poorer linearity of metaphase accumulation was observed and the duration of linearity was reduced sometimes to 2–2 1/2 h. Overall, under these circumstances, estimation of average CCPR was more precise by the single time point accumulation method. More importantly, significant differences were sometimes evident between the results of these two methods when applied to the same data.