Milk urea-N is used by dairy nutritionists and producers to monitor dietary protein intake and is indicative of N utilization in lactating dairy cows. Two experiments were conducted to explore discrepancies in MUN results among 3 laboratories and one experiment to evaluate the effect of 2-bromo-2-nitropropane-1,3-diol (bronopol) on MUN. In Experiment 1, 10 replicates of bulk tank milk samples, collected from the Pennsylvania State University’s Dairy Center over 5 consecutive days, were sent to 3 milk processing laboratories located in Pennsylvania. Average MUN differed (P ≤ 0.05) between Laboratory A (Foss 4000; 14.9 ± 0.40 mg/dL), Laboratory B (Foss FT + 600; 6.5 ± 0.17 mg/dL), and Laboratory C (Foss 6000; 7.4 ± 0.36 mg/dL). In Experiment 2, milk samples were spiked with urea at 0, 17.2, 34.2, and 51.5 mg/dL of milk. Two 35-mL samples from each urea level were sent to the 3 laboratories used in Exp. 1. Average analyzed MUN was higher than expected (calculated for each laboratory based on the control; 0 mg added urea): for Laboratory A (23.2 vs. 21.0 mg/dL; P = 0.001), Laboratory B (18.0 vs. 13.3 mg/dL; P < 0.001), and Laboratory C (20.6 vs. 15.2 mg/dL; P < 0.001). In Experiment 3, replicated milk samples were preserved with 0 to 0.30 g bronopol/35 mL milk (at 0.02 g increments) and submitted to one milk processing laboratory that analyzed MUN using 2 methods. Samples with increasing amounts of bronopol ranged in MUN concentration from 7.7 to 11.9 ± 0.27 mg/dL (linear increase due to bronopol; P < 0.001) and from 9.0 to 9.3 ± 0.05 mg/dL (P = 0.06) when analyzed on Foss 4000 or CL10, respectively. In this experiment, bronopol was calculated to contribute 7.9% of the total N in milk for the average milk vial (0.21 ± 0.003 g bronopol/ 35 mL milk) when milk protein was 3.01% and MUN was 8.5 mg/dL. In summary, MUN concentrations vary due to analytical procedures used by the milk processing laboratories. Amount of bronopol used to preserve the milk sample may also have an effect on MUN. Thus, it is important to maintain consistency in milk sample preservation and analysis to ensure precision and accuracy of MUN results.