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We examined the relationship between, and variations in, particulate organic carbon (POC) and particulate organic nitrogen (PON) based on previously acquired ocean and inland water data. The latitudinal dependency of POC/PON is significant between 20 and 90° N but weak in low-latitude areas and in the Southern Hemisphere. The mean values of POC/PON in the Southern Hemisphere and Northern Hemisphere were 7:40±3:83 and 7:80±3:92, respectively. High values of PON/POC appeared between 80-90 (12:2±7:5) and 70-80° N (9:4±6:4), while relatively low POC/PON was found from 20 (6:6±2:8) to 40° N (6:7±2:7). The latitudinal variation of POC/PON in the Northern Hemisphere is much stronger than in the Southern Hemisphere due to the influence of more terrestrial organic matter. Higher POC and PON could be expected in coastal waters. POC/PON growth ranged from 6:89±2:38 to 7:59±4:22 in the Northern Hemisphere, with an increasing rate of 0.0024 km from the coastal to open ocean. Variations of POC/PON in lake water also showed a similar latitude-variation tendency of POC/PON with ocean water but were significantly regulated by the lakes' morphology, trophic state and climate. Small lakes and high-latitude lakes prefer relatively high POC/PON, and large lakes and low-latitude lakes tend to prefer low POC/PON. The coupling relationship between POC and PON in oceans is much stronger than in inland waters. Variations in POC, PON and POC/PON in inland waters should receive more attention due to the implications of these values for the global carbon and nitrogen cycles and the indeterminacy of the relationship between POC and PON. [ABSTRACT FROM AUTHOR]