Different sample pretreatment and extraction techniques are often used for analysis of nitrates and nitrites, however, the effects of these variables have not been properly examined. Comparative investigations were carried out with the objective of finding the most suitable conditions for quantification of nitrate and nitrite in spinach and lettuce. A rapid and cost effective RP-HPLC/UV method was validated and used to select the most appropriate extraction procedure to eliminate chromatographic interferences and to evaluate the influence of different sample pretreatments on the accuracy and reproducibility of the results obtained. Similar nitrate concentrations were obtained for fresh and two weeks frozen samples. Freeze drying and oven drying pretreatment of the spinach and lettuce material was inappropriate. No nitrite was detected in either fresh, freeze dried, oven dried, and frozen spinach or lettuce. lt;br> lt;br> Keywords: lettuce; nitrate; nitrite; RP-HPLC/UV; spinach lt;br> lt;a target="_blank" href="http://www.informaworld.com/smpp/content~db=all~content=a919596269~frm=titlelink "> Texto integral lt;/a> lt;br> lt;br> Different sample pretreatment and extraction techniques are often used for analysis of nitrates and nitrites, however, the effects of these variables have not been properly examined. Comparative investigations were carried out with the objective of finding the most suitable conditions for quantification of nitrate and nitrite in spinach and lettuce. A rapid and cost effective RP-HPLC/UV method was validated and used to select the most appropriate extraction procedure to eliminate chromatographic interferences and to evaluate the influence of different sample pretreatments on the accuracy and reproducibility of the results obtained. Similar nitrate concentrations were obtained for fresh and two weeks frozen samples. Freeze drying and oven drying pretreatment of the spinach and lettuce material was inappropriate. No nitrite was detected in either fresh, freeze dried, oven dried, and frozen spinach or lettuce.