The leaching of phthalate plasticizers from four types of blood platelet bags was investigated. The anticoagulant solutions used in the blood collection bags had pH values of 5.64 +/- .04 and contained no detectable amounts of phthalates. Platelet bag materials from each bag were soaked in normal salines for up to 5 days. The salines were tested for the leached phthalates from the bags but none could be found. However, di-(2-ethylhexyl) phthalate (DEHP) leached out of the PL-146 and Terumo bags into bovine calf serum used for soaking the bag materials. There was an increase in the amount of DEHP leached from about 1.1 mg at the end of one day to about 3.3 mg per gm of bag material at the end of a five day extraction with the serum. In PL-732 sets, a platelet bag made of a specialty polyolefin, the amount of DEHP leached out was less than 0.02 mg per g of bag material. CLX bags, which contained tri-(2-ethylhexyl) trimelliate (TETM) as a plasticizer, showed a negligible amount of it leaching into the calf serum. Infra-red spectra showed that PL-146 bags had been coated with a layer of a fatty acid amide while the Terumo bags contained a layer of a silicone fluid on their inner surfaces. CLX bags showed a coating of stearates, which were probably soaps of calcium or zinc. Scanning electron microscopy (SEM) showed that the inner surfaces of each brand of the bag were distinctly different morphologically. The two PVC bags were very similar whereas the surfaces morphology of PL-732 was rougher. Terumo bag had a different surface morphology than those of the other bags whereas the CLX bags had a very regular surface pattern. The exact significance of the surface morphology is not certain but excessively rough surfaces may not be desirable for the bags.