Amniostat-FLM is a recently developed rapid slide agglutination test for amniotic fluid phosphatidylglycerol. We compared phosphatidylglycerol quantitated by two-dimensional thin-layer chromatography with phosphatidylglycerol determined by Amniostat-FLM in 180 amniotic fluid samples. If any level of phosphatidylglycerol by thin-layer chromatography, including a trace, was considered positive, then phosphatidylglycerol by thin-layer chromatography and Amniostat-FLM were concordant in 171 of 180 samples (95%). Both were positive in 123 and both negative in 48 samples. The nine amniotic fluid samples with discrepant results were as follows: Five negative Amniostat-FLM results were associated with trace phosphatidylglycerol by thin-layer chromatography (1% to 2% of total phospholipids), one negative Amniostat-FLM result was associated with 3% phosphatidylglycerol by thin-layer chromatography, and three positive Amniostat-FLM results were associated with negative phosphatidylglycerol by thin-layer chromatography results. There were 14 samples with trace phosphatidylglycerol by thin-layer chromatography; of these, there were nine positive and five negative Amniostat-FLM results. If greater than 2% phosphatidylglycerol by thin-layer chromatography was considered positive, concordance between the two tests was 93% (167 of 180). From these samples, 119 infants were delivered within 72 hours of amniocentesis. There were 100 positive Amniostat-FLM results and all were associated with the absence of respiratory distress syndrome; of the 19 negative Amniostat-FLM results, five were associated with infants who developed respiratory distress syndrome. The present study confirms that Amniostat-FLM is a simple, rapid, and accurate test for determining the presence of phosphatidylglycerol in amniotic fluid.