| alpha-Lactalbumin, [methyl-14C]- Discontinued | MC 1481 |
| Lactose, [D-glucose-1-14C]- | MC 1466 |
| Lactose, [D-glucose-14C(U)]- | MC 1479 |
| Laflunimus, [14CN]- | MC 2791 |
| Lamivudine | M 975 |
| Lamivudine triphosphate, tetraammonium salt | M 395 |
| Lamotrigine, [3H]- | MT 2158 |
| Lamotrigine, [3H]- | MT 2158L |
| Lapatinib, [3H]- | MT 2002 |
| Lauric acid, [1-14C]- | MC 2208 |
| Lauryl isethionate, sodium salt, [isethionate-14C]- | MC 2386 |
| Lauryl isethionate, sodium salt, [lauryl-1-14C]- | MC 2384 |
| N-Lauroylsarcosine, [3H]- | MT 1706 |
| D,L-Leucine, [1-14C]- | MC 2405 |
| L-Leucine, [14C(U)]- | MC 175 |
| L-Leucine, [14C(U)]- | MC 175A |
| L-Leucine, [14C(U)]- | MC 175W |
| L-Leucine, [1-14C]- | MC 404 |
| L-Leucine, [1-14C]- | MC 404E |
| L-Leucine, [4,5-3H]- in 0.01N HCl ; 60-120 Ci/mmol | MT 672 |
| L-Leucine, [4,5-3H]- in Ethanol:water (2:98) ; 60-120 Ci/mmol | MT 672E |
| L-Leucine, [4,5-3H]- in Ethanol:water (2:98) ; 5 Ci/mmol | MT 672EL |
| L-Leucine, [4,5-3H]- | MT 672M |
| (6S)-Leucovorin, diammonium salt, [3',5',7,9-3H(N)]- Discontinued | MT 521 |
| (6S)-Leucovorin, diammonium salt, [3H]- | MT 2187 |
| Lignoceric acid, [1-14C]- | MC 1315 |
| D-Limonene, [CH2-14C]- | MC 2749 |
| Linalool, [3H]- | MT 1775 |
| Linolenic acid, [1-14C]- | MC 2197 |
| Lithium acetate, [2-14C]- | MC 1422 |
| Lopid, [carboxyl-14C]- | MC 455 |
| Lobucavir, [3H]- | MT 1530 |
| Lopinavir | M 1735 |
| Lopinavir, [phenoxyacetamido-acetamido-14C]- | MC 2477 |
| Lopinavir, [3H]- | MT 1648 |
| Luciferin, [benzene-14C(U)]- | MC 2127 |
| Lumacaftor, [3H]- | MT 2102 |
| Luteolin, [6,8-3H(N)]- | MT 1559 |
| Luteolin, [3H]- | MT 1917 |
| L-Lysine, [14C(U)]- | MC 197 |
| L-Lysine, [4,5-3H(N)]- | MT 909 |
| L-Lysine, [4,5-3H(N)]- | MT 909L |
| L-Lysine, [4,5-3H(N)]- | MT 909W |
| Lysine methyl ester, [3H]- | MT 1935 |
| D-Lys-Pro-Thr, [3H]- | MT 1913 |
| 9-(α-L-Lyxofuranosyl)-2-fluoroadenine, [8-3H]- | MT 1763 |
| D-Lyxose, [1-14C]- | MC 2332 |