An assessment was made of the stability of nine total nutrient admixtures (TNA) for total parenteral nutrition (TPN) and of Intralipid 20% filtered through a 5-micron filter. Mixture samples from 3-litre EVA plastic bags were obtained for tests 4 and 24 h after preparation, before and after filtration through a 5-micron filter during a period of 24 h. The filtered mixtures were collected in 3-litre EVA plastic bags and the contents of the filter were also examined. Stability parameters studied were pH, lipid globule size and visual signs of emulsion breakage. Used for assessment of lipid globule size were a light microscope and a Coulter Counter TA II, which measures particles from 1.4 microns to 43.8 microns in diameter. There were no physical signs of instability in any of the mixtures tested while they were being filtered and collected through the 5-micron filter. Examination of mixture samples prior to filtration and of filter contents revealed the presence of large fat globules, precipitates, solid particles and aggregates. Although these were trapped on the surface of the filter there was no slowing of the rate of flow of the mixture. These findings demonstrate the importance of using a 5-micron filter in delivering total nutrient mixtures in order to avoid the hazards posed by the presence of particles larger than 5 microns in size and show that its use does not affect stability.